The marvelous beauty of sea-shells and tropical land-shells,

their almost infinite variety in form and coloring, has given to

them an interest among collectors that is very great. There are

many wonderful conchological collections in public museums and in

private cabinets. It would well repay the lover of beauty as well

as the more serious student of nature to examine carefully such

collections when opportunity offers, for nowhere in the realm of

nature can more exquisite coloring and modeling be found. The fact

that shells may be preserved for all time without the expense and the

vexations of preservative fluids has no doubt induced many [pg307]

to choose this field of natural history for special study. But the

true student of zoölogy does not confine his investigations in this

phylum to considerations of the shell only, for the protective

armor constitutes only a portion, although an important portion, of

the anatomy of the mollusk. On the same principle, it would hardly

suffice to examine only the skeleton of vertebrate animals in order

to become acquainted with the fishes or mammals. In a sense, the

testaceous covering of a mollusk may be likened to an outer skeleton.

The older zoölogists were inclined to ignore almost entirely the

animal or "soft parts" of mollusks, and their classification of

the phylum into "univalve," "bivalve," and "multivalve," based

upon shell-characters alone, has since been proved to be wholly

artificial. The terms "univalve" and "bivalve" are, of course, often

and correctly used to-day to designate mollusks possessing a single

or a double shell, such as the common garden-snail, which carries

upon its back a single spiral shell, and, on the other hand, the

oyster or clam, which is inclosed within two valves which fit closely

together. But these terms are not /technically/ used, although

they do indicate in a general way the more modern classification.

Even among some comparatively recent conchologists a tendency to

belittle the value of the "slimy creature" within the shell has led

to some curious errors of grouping--mistakes which more thorough

and scientific investigation has brought to light. In general, the

higher classification into classes, orders, suborders, and families

is exclusively based upon anatomical features, and to a large extent,

also, is that of the genera; but species are always determined by

their shell or conchological characteristics.

When a certain familiarity with the forms and general appearance of

shells is gained, a glance at the shell alone will almost always

suffice to place it at once in its true generic position, for, along

with modifications of the animal itself, corresponding modifications

of the shell are quite certain to take place. Hence a fairly expert

zoölogist should be able to determine with considerable accuracy from

an empty and dead shell the anatomical features of the animal that at

one time inhabited it. [pg308]

One of the main reasons for the special interest that seems to have

attached to the study of conchology is derived from the fact that the

durability of shells has caused their almost perfect preservation

as fossils from the very earliest periods of geological time, thus

furnishing the key to the solution of many problems of evolution.

Upon this page of the earth's history the letters are sharp and

clear, and geologists possessing a knowledge of recent forms of

mollusks as well as of their geographical distribution have been

enabled to read some wonderful stories of the cosmic history of

islands and continents.

GEOGRAPHICAL DISTRIBUTION

Mollusks are found in every part of the world. The arctic seas

possess their own characteristic faunæ, the more temperate waters of

Europe and of America contain their own peculiar genera and species,

and the warm waters of the tropic seas furnish the conditions

favorable to the life of an immense number of characteristic forms.

Again, there are the littoral species, that live only between

tide-marks and are therefore exposed to the air for a number of

hours each day; some of these live just about high-tide mark and

have become almost terrestrial in their habits, while others must be

sought at the point of lowest tide, where for only a short time each

day they are deprived of their natural element. Then there are the

shallow-water forms, which never appear above low-tide mark save when

a neap tide surprises them; their range in depth extends to about

the hundred-fathom line, more or less. Beyond this depth to several

hundred fathoms other characteristic forms appear, and from the more

profound depths of mid-ocean the dredge has brought to light a host

of curious and interesting species.

It is the temperature of the water rather than the depth that appears

to influence the distribution of marine mollusks. Thus, certain

species whose natural home is in the shallow waters of the Arctic

Ocean have been taken in very deep waters off the southern coast of

the United States, the temperature conditions in both stations being

substantially the same. This fact, however, must not be too freely

accepted as establishing a principle. Some [pg309] shallow-water

forms have been taken at great depths, but in general the abyssal

fauna is a peculiar one that cannot well be marked off into

geographical provinces.

THE ARCTIC PROVINCE

The east coast of America is divided into several molluscan

faunal regions. A series of very-cold-water forms belonging to a

circumpolar region, called the "arctic province," are found as far

south as Newfoundland. On the New England coast a number of these

arctic species are also found, urged south by the influence of the

cold Labrador current. The most characteristic genera belonging to

this arctic fauna which are found upon the Maine and Massachusetts

coasts are /Buccinum/, /Chrysodomus/, /Sipho/, /Trophon/, /Bela/,

/Velutina/, /Trichotropis/, /Lacuna/, /Margarita/, /Pecten/, /Leda/,

/Yoldia/, /Astarte/, and /Mya/. Examples of all these genera are

encountered as far south as Cape Cod.

THE BOREAL PROVINCE

A "boreal province" corresponds with a similar faunal region upon

the European shore. The mollusks which compose this fauna are about

three hundred in number, and range along the New England coast from

the Gulf of St. Lawrence to Cape Cod. It is a somewhat remarkable

fact that many of these species are identical with English and French

forms. The striking genera upon the American side are /Purpura/,

/Littorina/, /Polynices/ (/Lunatia/ and /Neverita/), /Acmæa/,

/Margarita/, /Chiton/, /Doris/, /Æolis/, /Mytilus/, /Modiola/,

/Thracia/, and /Nucula/.

THE TRANSATLANTIC PROVINCE

Cape Cod has been regarded, until very recently, as a sharp

divisional point between the boreal and the transatlantic provinces,

the latter faunal area extending down the Atlantic coast of the

United States to southern Florida. At Cape Cod the Labrador current

is deflected from the coast, and the warmer shore waters south of

that point are unfitted for the development of the boreal forms,

though some of them, as we shall see, have passed the [pg310]

barrier and maintain themselves very successfully at Martha's

Vineyard and in Long Island Sound. Some of the species whose natural

habitat is south of Cape Cod are also to be found north of that

point, but they do not reach their full development in the colder

waters of Massachusetts Bay.

The long stretch of coast-line from Cape Cod to Florida is easily

susceptible of faunal subdivision at Hatteras, below which locality a

decided mixture of Antillean species is apparent. Between Long Island

Sound and Hatteras the littoral molluscan fauna is disappointing

to the collector, for the number of species is relatively small,

and few even of these are entitled to any claims to beauty of

shell. The nature of this coast, virtually a great sweep of exposed

sand-beach, is not conducive to a varied or rich fauna. But if this

portion of the transatlantic province is lacking in interest to

the shell-collector, it is anything but disappointing to the army

of men employed in the oyster- and clam-fishery. It is only within

this faunal area that the American oyster, /Ostrea virginica/, the

best of the edible shell-fish, finds its natural home, and here the

oyster-culture is most extensively carried on.

After storms the Jersey beaches are frequently strewn with /Mactra/,

/Tagelus/, /Arca/, and /Ensis/; in more sheltered places /Fulgur/ and

/Polynices/ (/Lunatia/) are commonly met. These may be accepted as

the most characteristic genera of this province.

Just south of Cape Hatteras an observer is struck with the sudden

change in the appearance of the shells on the beach. /Cardium/,

/Cassis/, /Dolium/, /Arca/, and /Cancellaria/ at once suggest

the West Indies. About the vicinity of Hatteras the Gulf Stream

approaches very near the land, bringing with its warm waters many

wanderers from tropical homes. From Beaufort to Florida there is

another long stretch of exposed and shifting sand-beach, which offers

a scant return to the collector of mollusks.

THE CARIBBEAN PROVINCE

When Florida is reached a new world is opened to the naturalist,

for there a better acquaintance is made with the great Caribbean

province, which, extending from Florida to the northern shores of

South America, embraces all the Bahamas, the West [pg311] Indies,

the Gulf of Mexico, and the coast of Central America. Strangely

enough, the mollusks of the west coast of Florida are more nearly

related to those of the transatlantic province than are the shells

of the east Florida coast. This remarkable fact in geographical

distribution can only be explained by assuming that an open waterway

once existed across the northern part of the Florida peninsula,

connecting the Atlantic and the Gulf, through which a mingling of the

shallow-water forms from Georgia, the Carolinas, West Florida, and

the Gulf coast took place. Thus it would appear that when Florida

was an island the fauna of its east coast, originally largely

Antillean, was less disturbed by the southern migration of American

species. The Florida Keys are essentially Antillean. The Caribbean

or Antillean fauna is an exceedingly rich and varied one. Among the

most prominent genera which may be encountered upon the Florida coast

are /Strombus/, /Fasciolaria/, /Oliva/, /Marginella/, /Natica/,

/Sigaretus/, /Littorina/, /Tectarius/, /Neritina/, /Melongena/,

/Cardium/, /Callista/, /Tellina/, /Lucina/, and /Cyrena/. In such an

extensive and rich faunal province one must not expect to find in any

given locality a representation of all the characteristic genera. For

instance, collections made at Havana, at Nassau, and at Vera Cruz

would each contain forms more or less peculiar and local, but certain

species would be found in each collection.

* * * * *

On the west coast of America quite the same faunal division into more

or less well-marked provinces is to be found. Bering Sea belongs to

the arctic province, and contains, with Labrador and Greenland, many

identical forms.

THE ALEUTIAN PROVINCE

The shore waters from the southern peninsula of Alaska down to about

Vancouver comprise the Aleutian province. Within this area occur

some arctic species, notably the soft-shell clam, /Mya arenaria/,

which the fishermen gather in such large quantities for bait along

the Maine coast. An increasing number of species common to this

west-coast faunal region and to the boreal province of the east coast

are being recorded. Some of [pg312] these have been introduced from

the East by the agency of man, but others no doubt have a natural

range through the icy waters north of America and down through the

Bering Sea into the Pacific.

THE CALIFORNIAN PROVINCE

The Californian province extends from the neighborhood of Vancouver

to Cape St. Lucas and has about five hundred species. The northern

portion of this area contains some very characteristic forms,

together with a good mixture of species of more northern habitat;

it might properly be regarded as a subprovince. From San Diego

south to the cape the character of the fauna gradually changes;

this coast-line of southern California has also been considered a

subregion. The main characteristic of the Californian province is a

large development of /Haliotis/, of the patelliform mollusks, and

of the chitons. A very few minutes on any good collecting-beach

of California would convince the Eastern conchologist that he had

entered upon an entirely new field of research. The most notable

genera are /Calliostoma/, /Chlorostoma/, /Scurria/, /Acmæa/, various

genera of the /Chitonidæ/, /Purpura/, /Monoceras/, /Amphissa/,

/Norrisia/, /Olivella/, /Chorus/, and /Haliotis/.

THE PANAMIC PROVINCE

The warmer waters of the Gulf of California belong to the Panamic

province, which extends down to South America. This is one of the

richest and most interesting faunas in the world. At Panama alone,

Mr. C. B. Adams, a noted collector and student of conchology, took

upward of four hundred species. About eight hundred species are known

in the Gulf of California alone.

* * * * *

It must be borne in mind that these faunal provinces relate to

littoral and shallow-water species, for the present knowledge of

deep-water forms is not sufficient to permit of generalization upon

their distribution.

We review here only the conspicuous forms along our own coasts. It

may be well to note, however, that in some other parts of the world

the development of molluscan life is far [pg313] in excess of

anything to be found upon our shores. The veritable paradise of the

naturalist is the East Indies. There the "aristocratic" genera, so

called on account of their marvelous beauty, occur in their highest

development--/Voluta/, /Mitra/, /Oliva/, /Conus/, and the various

murices. There also are to be found the pearl-oysters, /Meleagrina

margaritifera/, that yield their valuable harvest, and the giant

clam, /Tridacna gigas/, which measures sometimes five feet in

length. Over eight thousand species of mollusks are described from

this surpassingly rich region, yet this vast province, as compared

with the American and European shores, has been but superficially

exploited by the naturalist. In whatever part of the world a

naturalist may find himself, there is always a tempting array of

molluscan life to attract him. Each fauna possesses features peculiar

to itself, and from the point of view of the true naturalist, the

more somber-hued and conventionally formed mollusks of Northern

shores are no less interesting than the gorgeously tinted and

fantastically shaped species of the tropics. From any faunal province

of our own country one may readily gather all forms necessary to

furnish ample material for study from which one may acquire an

excellent idea of the biological features of the entire phylum.

STATION AND HABITS OF THE MOLLUSCA

The word "station" is used to indicate the nature of the surroundings

which an animal chooses as most suited to his well-being. Some groups

of mollusks, like the littorinas, the trochids, the purpuras, and the

majority of those having patelliform shells, generally live on rocks

above low-tide mark; other genera, like /Buccinum/, /Sipho/, and

/Chrysodomus/, prefer rocky or gravelly ground below low-tide mark.

Other mollusks burrow deep in the mud, many prefer sandy bottoms,

while a host of other species seek homes upon the tangled masses of

seaweed, living like arboreal creatures in the submarine forests.

Nearly every conceivable character of sea-bottom or shore-line

between tides harbors its own peculiar types of molluscan life. There

are some very curious genera of bivalves that bore their way into the

hardest rock and [pg314] there find a comfortable shelter for life.

A numerous class of pelagic or free-swimming mollusks supposedly

never go to the bottom at all, but spend the whole of their existence

on or near the surface of the sea, always in open water, where

their fragile shells may not be injured by rough contact with solid

substances.

The food of some is vegetable, of others, animal. The bivalves, like

the clams, oysters, cockles, and mussels, feed only on microscopic

organisms. They create a current of water through their siphons, or

mantle openings, and then, by a process best known to themselves,

catch and swallow all the animalculæ thus brought to their mouths.

The univalves which possess a siphon are, for the most part,

carnivorous, and are often most voracious creatures. They feed upon

any animal matter they can find, while some of them are enabled by

means of a sharply toothed tongue to bore through the solid shells

of other mollusks and extract the succulent vitals from within. One

energetic little mollusk in particular, /Urosalpinx cinerea/, is

for this reason a great pest upon the oyster-beds. Univalves not

possessed of a siphon may generally be considered herbivorous; they

pass most of their time peacefully browsing upon algæ.

Mollusks are all oviparous or ovoviviparous; that is, they lay eggs,

or, laying eggs, they retain them within their shells until the

young are hatched out. As a rule, each species of mollusk has its

own particular method of protecting its eggs from external injury.

Some construct tough, leathery capsules which are strung together in

various patterns. The egg-capsules of /Purpura lapillus/, resembling

little pinkish or yellowish club-shaped stalks, may frequently

be found in the crevices of rocks and under the rockweeds. The

egg-cases of /Polynices/ (/Lunatia/) are most peculiar, resembling

inverted gelatine-bowls with the bottom knocked out; when wet they

are semi-elastic translucent masses in which may be seen myriads of

eggs. /Buccinum undatum/ arranges its hemispherical egg-capsules

in layers one above the other. The number of eggs so deposited is

often very great, running well into the thousands. Egg-capsules of

/Fulgur/ are leathery coils of angular disks adhering by one edge to

a connecting-band of a similar texture. (See Plate I.) [pg315]

In bivalves the eggs are retained within the parent shell until

hatched, and the young, which then escape into the water, are very

different-looking creatures from the parent. Generally the young

bivalve is free-swimming and exceedingly lively in its movements;

sometimes by means of cilia it is enabled to attach itself to any

passing host, and thus the species is widely disseminated. The fry

soon lose their embryonic form and take on the characteristics of the

adult.

The longevity of mollusks varies greatly with the species. Some

attain an age of from ten to fifteen years, while some are only

annuals. Oysters continue to grow for four or five years, after

which they may survive many years more. In truth, little is known

concerning the duration of life even of our better-known shore

species.

In point of intelligence, mollusks must be relegated to a very

low position. They give evidence of possessing no more than

the most primary instincts, those of self-preservation and of

reproduction. There are some forms that exercise a high degree of

protective mimicry. The highest class of mollusks, the /Cephalopoda/

(cuttlefishes, octopi, etc.), is widely separated from the other

classes in the development of faculties that appear to correspond

with intelligence. They are exceedingly crafty in the pursuit of

their prey as well as in eluding capture.

STRUCTURE OF MOLLUSKS

Among the invertebrate animals, especially in the lower orders, wide

physiological departures from central or typical forms are frequent.

It often happens that a whole group or even suborder will differ

so materially in its general characteristics from another group

or suborder belonging to the same phylum that the student will be

puzzled at first to understand how the two can be nearly related. In

many such cases it is only when the essential features of the phylum

are thoroughly understood that the relationships of its suborders

can be appreciated. An example of widely divergent groups within the

same phylum has already been shown in the /Echinodermata/. Who would

at first suppose that the graceful /Astrophyton/ could bear kinship

to the inert [pg316] holothurian, or that both of these have the

closest family ties with the sea-urchins?

The probable reason for these startling departures from a typical

form is that in the lower orders of life, where the organs and their

functions are comparatively simple, the laws of evolution operate

far more quickly in the adaptation of an organism to environment and

changed conditions of life. A decided tendency to this departure from

the type is a feature of the mollusks. It would be difficult, if

not impossible, to give a general description that would fit both a

common garden-snail and the common oyster, yet both are mollusks. A

concise definition of the phylum is therefore practically impossible,

and it seems here as if nature resented all attempts to circumscribe

her living forms by rigid rules.

The most persistent characteristic of the /Mollusca/ is the

possession of the "mantle," a sort of outer skin which, like a bag or

sack, envelops the creature above and about the sides, but is open

below, permitting the animal at will to protrude or withdraw its

foot. From the outer surface of this sheath-like mantle, or fold, a

calcareous shell is secreted. The modifications of this mantle are

infinite; indeed, in some well-marked groups it seems to have wholly

disappeared, having in reality become fused to the sides of the

animal, and having become therefore a mere outer skin, and no longer

a tunic or cloak, as originally intended. As already noted, the

mantle does not always secrete a shell, a fact which again reminds us

that we cannot give a good comprehensive description of the phylum

that always holds true throughout its subdivisions. The best that can

be done is to give in general terms the characters which appear in

a majority of the forms. A convenient method of going about this is

to create, for the sake of clearness, an ideal, model, or fanciful

mollusk and clothe it with all the most salient molluscan features,

and from such a basis to develop, as we go on, the various types of

the actual orders and suborders. There is one class of mollusks,

the /Amphineura/, which conforms reasonably well in most of its

features to our comprehension of the schematic mollusk. This class is

sometimes referred to by biologists as the "primitive" or "original"

mollusks, from which all the other classes have since been derived;

but the [pg317] evolutionary history of the development of the

various molluscan orders through geological time does not seem to

bear out the fact that an "ideal" mollusk, as we shall construct him,

ever actually existed, or that his prototype, the /Amphineura/, was

the first and consequently the ancestral type of the phylum. We must

therefore only accept this ideal mollusk theoretically, to serve as

a guide for the time being. We may profitably use it only as a lay

figure--a sort of manikin, which will introduce us to the phylum.

After our introduction we must forget our imaginary type and abandon

any notion we may have conceived of the parental position of the

/Amphineura/, its closest imitator in actual life.

THE IDEAL MOLLUSK

The ideal mollusk has a compact, somewhat elongated body, the under

or ventral portion of which is thickened into a muscular disk, upon

which it creeps along. This disk is called the /foot/. (Note a snail

thus crawling upon his "foot.") The foot is rounded or obtusely

pointed posteriorly. Forward, the body is slightly narrowed into

a neck, and then expanded again into a head. Upon this head are

carried two projecting, mobile, fleshy tentacles, one upon each

side, that superficially resemble two horns. At the base of each

tentacle, upon the inner side, is an eye. Just below and between the

tentacles is a small horizontal slit,--the mouth,--the lips being

slightly thickened. The visceral portion of the animal is above the

foot, or /dorsal/ to it, and extends the whole length of the animal

from the mouth to the excretory opening, the latter being situated

posteriorly. The visceral cavity is inclosed above by a thin skin;

indeed, it is but the great thickening of this skin below that

constitutes the foot.

[Illustration: Ideal or schematic mollusk.

1, dorsal view: /h/, head; /t/, cephalic tentacle; /sh./, shell

covering visceral mass; /b.m./, outline of body-mass; /r.m.e./,

edge of mantle; /c.t./, ctenidia, or gills; /q.a./, generative

apertures; /r.e./, renal openings; /e.o./, excretory opening; /f/,

posterior portion of foot; /o.e.m./, edge of shell.

2, ventral view: /h/, head; /t/, tentacle; /m/, mouth; /b/, outline

of body; /e.m./, edge of mantle; /s.f./, lower surface of foot;

/c.t./, ctenidia, or gills; /f/, posterior portion of foot.

3, horizontal section, showing heart, nephridia, and gonads:

/m/, mouth; /o/, esophagus; /g/, gonad; /p/, pericardium; /n/,

nephridium, or renal organ; /v/, ventricle; /a/, auricles; /g´/,

gonad aperture; /n´/, renal opening; /e/, excretory opening; /f/,

posterior portion of foot.

4, vertical median section: /m/, mouth; /b.m./, buccal mass; /l/,

liver; /d.a./, digestive tract; /q/, gonad; /f/, foot; /q.o./,

gonad aperture, or opening of oviduct; /r.o./, renal opening;

/e.o./, end of digestive tract, excretory opening; /n/, mantle;

/r/, nephridium, or renal organ; /o.f./, recurved portion of

mantle; /sh./, shell; /v/, ventricle; /p/, pericardium.]

The digestive tract, beginning at the mouth, opens immediately into a

muscular throat, which is called the /buccal mass/. Within the buccal

mass there is a long, fleshy ribbon that bears upon its upper surface

numerous rows of sharp teeth; these rows of teeth run crossways on

the ribbon, each row containing more or less prominent median teeth,

with several laterals upon each side, and with marginal teeth on each

side of the laterals. This is called the /radula/, and is used for

tearing or rasping the food. When [pg319] not in use it lies coiled

up within the buccal mass. Beyond the buccal mass, food passes into

the esophagus, which widens out into a muscular pouch or stomach;

this may also be provided with chitinous teeth or hard knobs or

plates for the purpose of further triturating the food. Above and

partially surrounding the stomach is a large reddish or brownish

liver, which furnishes to the alimentary canal the digestive juices.

From the stomach the intestine leads to the terminal anal opening.

There are two organs, serving the function of kidneys, placed

dorsally one upon each side of the body (/nephridia/). A heart lies

within the median line of the body, and consists of a ventricle and

two lateral auricles. The vascular system is almost entirely closed;

only in so far as it is partially open does it essentially differ

from that of higher groups; the blood is whitish or light bluish,

and receives its oxygenation in the gills or along the free mantle

surface, through which it courses in exceedingly thin capillaries. In

this manner respiration is carried on to some extent throughout the

whole outer surface of the body. There are two /branchiæ/ (gills).

These have the appearance of small feathers and are placed upon

each side of the animal posteriorly; they project slightly. Spread

over the top of this animal, fitting it perfectly, is a thin fleshy

covering attached to its dorsal portion like a skin, but hanging

free, like a flap, over the sides, the head, and the posterior end

of the animal. Upon the sides it may just cover the tips of the

branchiæ, but in front the head is seen to project from under it.

The loose-hanging portion of this sac-like covering is somewhat

thickened, and perhaps recurved upward upon itself. Upon the edge of

this flap all the way around may occur a row of cilia, or tentacular

processes. This cloak-like covering is called the mantle, and, as

already noted, is the most peculiar and persistent characteristic

of the /Mollusca/. The "cavity" formed between the loose-hanging

portion of the mantle and the sides of the foot is called the /mantle

cavity/, and contains posteriorly the gills, or branchiæ. From the

outer surface of this mantle a calcareous secretion takes place,

forming a shell, which, in our ideal mollusk, will be shaped in

conformity with the surface outlines of the mantle, oblong and convex

above. Over the lower portion of the shell the edge of [pg320] the

mantle recurves. When the creature is disturbed or is at complete

rest it may withdraw that portion of the mantle which protrudes from

below the shell entirely within the edge of the shell, so that the

"soft parts" may be wholly covered, and thus protected from harm. In

such a state of rest nothing may be seen from above but a shell. The

entire upper surface of the mantle is firmly attached to the under or

inner side of the shell, except the mantle margin, this being free.

The nervous system consists of a circumesophageal ring of

nerve-cells, with two cords passing along the digestive tract to the

posterior end of the animal. In the head and above the buccal mass

are several series of nerve-ganglia. These also communicate with the

posterior portion of the animal through two parallel cords which pass

along its ventral side. From these four principal branches, which

traverse the entire length of the creature, minor nerve-cords are

thrown off to the tentacles, the foot, the branchiæ, and the various

organs of the viscera. The sexes are separate.

Reviewing our "typical mollusk," we find that it is bilaterally

symmetrical--that is, uniform upon both sides of a median line from

mouth to excretory opening; is unsegmented; has the ventral surface

thickened into a creeping foot or disk; and is possessed of a head

with tentacular processes, a radula, lateral branchiæ, a heart with a

ventricle and two auricles, a well-developed mantle, and a shell.

If the reader can learn these few details of organization he knows

the structure of a mollusk. In turning to the actual living forms he

will find merely modifications (though sometimes confusing ones) of

these various parts.

CLASSIFICATION

The /Mollusca/ are divided into five great classes: /Amphineura/,

/Gasteropoda/, /Scaphopoda/, /Pelecypoda/, and /Cephalopoda/. These

names, it will be noticed, with the exception of the first, all refer

to the /foot/, the modifications of the foot being selected as the

basis of the first great divisions of the phylum. The /Gasteropoda/

crawl upon the thickened ventral surface of their bodies (already

[pg321] referred to as the foot), as the common garden-snail, the

periwinkles, and in general all those mollusks which have a spirally

coiled shell. The /Scaphopoda/ have a long, worm-like foot, with

which they burrow in the sand or mud. Their shells are like miniature

elephant-tusks, but are open at both ends. The /Pelecypoda/ have a

more or less club-shaped foot, utilized, in the many families, for

a great variety of purposes. They are always inclosed in a bivalve

shell. Familiar examples are the oysters, the clams, mussels, etc.

The /Cephalopoda/ have the /foot/ modified into a number of /arms/,

which encircle the head or the mouth. They are the cuttlefishes, the

octopi, squids, etc.

CLASS =AMPHINEURA=

ORDER =POLYPLACOPHORA=

The /Amphineura/, as already observed, approach most closely to the

ideal mollusk just described. They are bilaterally symmetrical.

This fact is so important that it constitutes them a class,

notwithstanding the fact that in respect to the foot (the basis of

division into classes) they would be included with the /Gasteropoda/,

for (barring some exceptional instances) they creep along upon a foot

quite as our ideal mollusk would, and as the /Gasteropoda/ do. The

head carries no tentacles, thus essentially differing in this respect

from the ideal form. The mantle is extended down in front, completely

covering the head. The branchiæ are confined to a few pairs of

/ctenidia/, or plume-like gills, within the mantle groove or cavity,

and are arranged upon each side of the excretory opening like small

feathers.

There are two orders of the /Amphineura/, the /Polyplacophora/ and

the /Aplacophora/ (or /Solenogastres/), the one name meaning "bearing

many plates," and the other "without plates," the word "plate" in

this sense being synonymous with "shell." The shell of the first

order consists of eight calcareous disks arranged in a longitudinal

row along the back or dorsal side of the animal, which overlap like

shingles on a roof and admit of great variation of form in the

various families. [pg322]

It will be observed from the examples given that the shell plates do

not entirely cover the mantle, but that a considerable portion of the

upper mantle surface is left exposed along the side of the animal.

This exposed portion of the mantle is called the /girdle/. It is

always very much thickened and is often exceedingly tough. In some

species it is covered by a great number of calcareous spicules or

granules which are embedded in the leathery mantle tissue. Strangely

enough, the /Chitonidæ/ (a large family of the /Polyplacophora/)

possess a great number of eyes scattered over the shell plates like

minute dots.

[Illustration: /Chiton spinosus/, dorsal view.]

The members of this order are to be found in all parts of the world,

but their greatest development is upon the west coast of America.

In California the student of marine life has a splendid opportunity

to examine the chitons. They are generally to be found adhering

to the under surface of stones about low-tide mark. They are very

sluggish in their movements and may readily be removed from their

resting-places by suddenly thrusting a knife-blade under the foot

and prying them off. When thus detached they have a habit of rolling

up into a ball and so remaining indefinitely; to prevent this they

should be placed at once in a jar of sea-water, where they will

resume their natural position. For preservation as cabinet specimens,

chitons should be tied down between two boards or flat substances,

to hold them firmly extended until dried; otherwise they are apt to

contract out of shape.

[Illustration:/Chiton/, ventral view: /an/, anus; /cten/, ctenidia;

/ft/, foot; /mant/, mantle-edge; /mo/, mouth.]

Six or eight species are exceedingly common upon the west [pg323]

coast. The collector who has successfully taken a number of these

will not fail to note the varying degrees of width of the girdle in

the different species. In some cases the girdle partially covers the

overlapping shell plates. The largest of all the chitons inhabits

the California shores and is known as ^Cryptochiton stelleri^.

It measures fully six inches in length and three in width. In

/Cryptochiton/ the girdle is continued over the shell plates as a

tough, gritty, brownish covering. The shell plates are white, and,

as detached pieces, are frequently to be found cast up upon the

California beaches, where, from their curious shape, they are often

referred to as "butterfly-shells."

[Illustration: /Chiton ruber./ /Chiton apiculatus./]

On the east coast of America there are comparatively few species, and

these are all small and inconspicuous. The three commonest ones are

^Chiton ruber^, ^C. albus^, and ^C. apiculatus^. They may readily be

found on stones or dead shells fished up from below low-tide mark, or

in rock-pools left by the receding tide.

ORDER =APLACOPHORA=

This second order of the /Amphineura/ is entirely destitute of the

shell plates characteristic of the first. The outer mantle surface,

however, develops a number of calcareous granules which correspond to

a shell. The /Aplacophora/ are symmetrical, having the mouth and the

excretory opening at the anterior and posterior ends respectively.

The foot is greatly modified, being narrowed at times to a mere slit

along the ventral surface. Some of them have long, worm-like bodies.

This is no doubt a very primitive form of mollusk, or, if not a

primitive form, it has greatly degenerated from some higher type.

They are supposed to be commensal in habit and live in the deeper

water offshore.

The /Aplacophora/ are not littoral animals, and it is extremely

unlikely that one will ever encounter them upon the beach, unless,

possibly, after the severest of storms. We may therefore leave them

with this mere mention and proceed to the second class of mollusks,

the /Gasteropoda/. [pg324]

TABLE SHOWING THE CLASSIFICATION OF THE GASTEROPODS AND SCAPHOPODS

DESCRIBED IN THIS CHAPTER

Phylum =MOLLUSCA=

Class =GASTEROPODA=

Order =OPISTHOBRANCHIATA=

Suborder =TECTIBRANCHIATA=

Families Genera Species

BULLIDÆ ^Bulla^ ^B. (Haminea) solitaria^

^B. occidentalis^

^B. nebulosa^

APLYSIIDÆ ^Aplysia^ ^A. Wilcoxii^

Suborder =NUDIBRANCHIATA=

DENDRONOTIDÆ ^Dendronotus^ ^D. arborescens^

ÆOLIDIDÆ ^Æolis^ ^Æ. papillosa^

DORIDIDÆ ^Doris^ ^D. bilamellata^

Order =PROSOBRANCHIATA=

Suborder =DIATOCARDIA=

Families Genera Species

ACMÆIDÆ ^Acmæa^ ^A. testudinalis^

^A. testudinalis,^

Var. ^alveus^

^A. mitra^

^A. patina^

^Lottia^ ^L. gigantea^

FISSURELLIDÆ ^Fissurella^ ^F. alternata^

^F. barbadensis^

^F. (Glyphis) aspersa^

^Lucapina^ ^L. crenulata^

HALIOTIDÆ ^Haliotis^ ^H. splendens^

^H. rufescens^

^H. cracherodii^

TROCHIDÆ ^Margarita^ ^M. cinerea^

^M. helicina^

^M. undulata^

^Calliostoma^ ^C. occidentale^

^C. jujubinum^

^C. annulatum^

^C. canaliculatum^

^C. costatum^

^Chlorostoma^ ^C. funebrale^

^C. brunneum^

^Trochiscus^ ^T. norrisi^

^Livona^ ^L. pica^

TURBINIDÆ ^Turbo^ ^T. castaneus^

Var. ^crenulatus^

NERITIDÆ ^Nerita^ ^N. peleronta^

^N. tessellata^

^N. versicolor^

^Neritina^ ^N. reclivata^

^N. viridis^

Suborder =MONOTOCARDIA=

JANTHINIDÆ ^Janthina^ ^J. fragilis^

SCALIDÆ ^Scala^ ^S. lineata^

^S. multistriata^

^S. groenlandica^

^S. angulata^

NATICIDÆ ^Polynices^ ^P. (Lunatia) heros^

^P. (Lunatia) triseriata^

^P. (Lunatia) lewisii^

^P. (Neverita) duplicata^

^P. (Neverita) recluziana^

^Natica^ ^N. clausa^

^N. canrena^

^Sigaretus^ ^S. perspectivus^

CAPULIDÆ ^Crepidula^ ^C. fornicata^

^C. plana^

^C. aculeata^

^Crucibulum^ ^C. striatum^

^C. spinosum^

LITTORINIDÆ ^Littorina^ ^L. litorea^

^L. rudis^

^L. palliata^

^L. irrorata^

^L. angulifera^

^L. scutulata^

^L. planaxis^

^Lacuna^ ^L. vincta^

^Tectarius^ ^T. muricatus^

^T. nodulosus^

CERITHIIDÆ ^Cerithium^ ^C. floridanum^

^C. muscarum^

^C. minimum^

^Bittium^ ^B. nigrum^

^Cerithidea^ ^C. scalariformis^

^C. sacrata^

VERMETIDÆ ^Vermicularia^ ^V. spirata^

STROMBIDÆ ^Strombus^ ^S. pugilis^

^S. gigas^

CYPRÆIDÆ ^Cypræa^ ^C. exanthema^

^C. spurca^

^C. spadacea^

^Trivia^ ^T. pediculus^

^T. quadripunctata^

^T. californica^

^T. solandri^

DOLIIDÆ ^Dolium^ ^D. galea^

^D. perdix^

^Pyrula^ ^P. papyratia^

CASSIDIDÆ ^Cassis^ ^C. tuberosa^

^C. cameo^

^C. testiculus^

^C. inflata^

Families Genera Species

MURICIDÆ Subfamily Muricinæ

^Murex^ ^M. rufus^

^M. pomum^

^Trophon^ ^T. clathratus^

^Urosalpinx^ ^U. cinerea^

^Eupleura^ ^E. caudata^

^Pteronotus^ ^P. festivus^

^Ocinebra^ ^O. poulsoni^

^O. lurida^

^O. interfossa^

^Cerostoma^ ^C. nuttallii^

^C. foliatum^

MURICIDÆ Subfamily Purpurinæ

^Purpura^ ^P. lapillus^

^P. patula^

^P. hæmastoma^

^P. crispata^

^P. lima^

^P. saxicola^

^Monoceras^ ^M. lapilloides^

^M. engonatum^

^Chorus^ ^C. belcheri^

COLUMBELLIDÆ ^Columbella^ ^C. mercatoria^

^C. (Anachis) avara^

^C. similis^

^C. (Astyris) lunata^

^C. (Amphissa) corrugata^

^C. (Astyris) gausapata^

NASSIDÆ ^Nassa^ ^N. trivittata^

^N. obsoleta^

^N. vibex^

^N. fossata^

^N. perpinguis^

^N. tegula^

^N. mendica^

BUCCINIDÆ ^Buccinum^ ^B. undatum^

^Chrysodomus^ ^C. decemcostatus^

^Sipho^ ^S. Stimpsoni^

^S. pygmæus^

^Siphonalia^ ^S. kellettii^

^Tritonidea^ ^T. tincta^

TURBINELLIDÆ ^Fulgur^ ^F. carica^

^F. canaliculata^

^F. perversa^

^F. pyrum^

^Melongena^ ^M. corona^

FASCIOLARIIDÆ ^Fasciolaria^ ^F. gigantea^

^F. tulipa^

^F. distans^

VOLUTIDÆ ^Voluta^ ^V. junonia^

MARGINELLIDÆ ^Marginella^ ^M. apicina^

OLIVIDÆ ^Oliva^ ^O. literata^

^O. mutica^

^Olivella^ ^O. biplicata^

^O. boetica^

CONIDÆ ^Conus^ ^C. floridanus^

^C. pealii^

CANCELLARIIDÆ ^Cancellaria^ ^C. reticulata^

Class =SCAPHOPODA=

DENTALIDÆ ^Dentalium^ ^D. dentale^

^D. pretiosum^

^D. hexagonum^

^Entalis^ ^E. striolata^

[pg328]

CLASS =GASTEROPODA=

The class /Gasteropoda/ is the largest and most comprehensive

subdivision of the /Mollusca/, and within its wide range of families

many differing details of organization are to be found. As a class it

possesses all the most characteristic features of the phylum, though

it is frequently modified in a high degree. This class includes

all the univalve mollusks (except /Nautilus/ and /Dentalia/), such

as the snails, the whelks, and the host of spirally coiled land,

fresh-water, and marine shells.

The gasteropod foot is, as has been remarked, primarily the same

as in our schematic mollusk--a flat, muscular disk caused by

the thickening of the ventral body-surface. The neck, head, and

tentacles are also quite the same, but considerable modification

of these organs will be found when we come to examine some

specimens. The mantle is always present, except in the nudibranch

or non-shell-bearing forms; but in few of the /Gasteropoda/ is the

mantle so regularly simple as in our ideal mollusk.

Perhaps the most striking feature of the /Gasteropoda/, and

one that will at first surprise him who has in mind the simple

structure of the ideal mollusk, is the fact that they are always

asymmetrical--that is to say, a median line drawn longitudinally

through a gasteropod will not divide it into halves of similar

anatomical structure.

The quality of symmetry is an important one throughout the lower

orders of animal life. In nearly all phyletic or class descriptions

the word "symmetry" occurs, and its exact meaning must be understood.

Take, for example, a human being; a median line drawn vertically

would divide him into two similar halves--upon each side would be

an eye, an arm, a leg, etc., of similar shape and construction. So

far at least as the external features [pg329] go, man is then a

symmetrical creature; likewise the vertebrates in general. Cases

of actual symmetry are found in the lobsters and crabs and in the

segmented worms. It is usual in describing mollusks broadly and in

general terms to call them symmetrical animals, yet here is the

largest class within the phylum, whose representatives are none of

them symmetrical. In the /Gasteropoda/ the mouth is anteriorly placed

in the head, just as in the ideal form, but the digestive tract,

after traversing the visceral cavity in the usual fashion, suddenly

turns forward and terminates in an excretory opening either on the

right or on the left side of the animal, just back of the head. The

various other orifices for the genital and renal glands are also

placed in this unexpected anterior position. The gills, or branchiæ,

are to be found upon one side only, forward of the heart, and

differ somewhat in appearance from the plume-like processes of the

/Amphineura/.

What, then, has become of the corresponding gill we should expect to

find on the other side? The symmetrical shape of the foot is not in

the least altered, but what has happened to cause this distortion of

the visceral portion of the animal? And, finally, will this torsion

of the body of the snail perhaps account for the spiral nature of the

shell?

An evolutionary process is supposed to have taken place in mollusks,

which, if real, would no doubt account for these curious conditions

of torsion in the /Gasteropoda/; but the theory upon which this

process is based is altogether speculative, and is not fully

sustained by the facts in the case. Originally all mollusks are

presumed to have been symmetrical, and are assumed to have resembled

very much in form the schematic creature we have already described.

Now, for some reason, certain of the primitive mollusks, but not all

of them, began to develop a larger visceral mass, which, continuing

to enlarge throughout many generations, began finally to protrude

above and form a hump on the dorsal side of the animal. This hump,

containing the liver, a portion of the intestines, and the generative

glands, as it increased in bulk became so much elevated that it could

no longer maintain itself in an erect position over the body, but,

impelled by its own [pg330] weight, began to sag over to one side.

Such a process would of course tend to twist the digestive tract and

bring the excretory opening constantly farther forward on one side.

At the same time, this process would necessarily interfere, by the

weight of the overhanging viscera and the shell covering the mass,

with the development of the branchiæ lying upon that side and now

crowded under the visceral mass. Thus, according to this theory, this

process has continued until, in the modern gasteropod, the digestive

tract has been bent upon itself and twisted from a straight course

into a curve of almost 180°, bringing the excretory opening near or

just over the head, where it empties into the mantle cavity; while

the original right gill, by the same movement, has been brought to a

position on the /left/ side of the head, forward of the heart, the

original left gill having been crowded out, eventually to atrophy and

disappear. The same torsion is found in the nerve-cords; the heart,

situated at about the pivotal position of this twisting process,

has turned about upon itself, leaving an auricle in front of the

ventricle, one auricle, like one of the gills, having been lost. The

mantle portion covering the visceral hump naturally continued to

secrete its shell, though always in conformity with the change, the

result being the familiar spiral form of the usual gasteropod shell.

This theory may not be satisfactory, but the asymmetry of gasteropods

is a problem to be solved, and a more interesting line of biological

investigation could not be found.

Let us now take a good example of a gasteropod and locate its various

organs; at the same time we may use the occasion to refer to more

important modifications of these organs which will be encountered

later in the various genera. The most available gasteropod on the

east coast of the United States for this purpose, is /Fulgur/, both

on account of its large size and its abundance. /Buccinum/ may be

used if the student is north of Cape Cod and therefore unable to

secure a good living specimen of /Fulgur/; the anatomical differences

between the two are slight.

Note the siphon protruding forward from a notch in the shell. This

consists merely in an elongation of a fold of the mantle, which is

held in a manner to constitute a tube, through which [pg331] the

animal draws in water to supply the gills, lying just back of the

siphon and concealed under the mantle in the cavity already spoken

of as the mantle cavity. With the exception of that portion of the

mantle which constitutes the siphon, no part of its margin, it will

be observed, can be seen, the edge of the shell completely hiding it

from view.

In some genera the siphon is exceedingly long--in fact, longer than

the body of the animal. In these cases the mollusk is generally fond

of burying itself in the sand and maintaining communication with

the world above only by means of this long, fleshy tube. In some

genera the siphon is protected by an elongation of the shell, as in

/Fasciolaria/ (Plate LXXVI). An extreme example of this is given in

the figure on page 343, which represents a species of /Murex/, where

the siphon is not only protected by the shell, but the shell itself

is further protected by the double row of sharp spines with which it

is beset.

[Illustration: /Buccinum undatum/: /si/, siphon.]

There are some genera which possess no siphons at all, in all of

which cases there is no notch in the shell opening, the aperture

being round, as in /Natica/ and in /Littorina/ (pages 368, 371). The

mollusks of this type make a fold in the forward part of the mantle

which serves as a siphon. Such a muscular folding in the mantle would

be technically called a /functional siphon/.

On the posterior dorsal side of the foot is attached a horny plate,

of concentric structure about a central or subcentral point or

nucleus. This is called the /operculum/, and serves to close the

entrance of the shell when the animal is withdrawn, the object no

doubt being protective. The opercula vary to a great extent in the

different genera; in some cases they are calcareous, in others

cartilaginous. When the aperture of the shell is very large it often

happens that the operculum does not entirely close the opening, as

in /Fulgur/, but in /Buccinum/ it is a close fit. The operculum is

entirely wanting in the /Pulmonata/, one of the [pg332] large orders

of the /Gasteropoda/. The figures represent some of the commoner

types of opercula.

[Illustration: Various forms of opercula. /Turbo/ (/Sarmaticus/).

/Turbo/ (/Callopoma/). /Livona./ /Ampullaria./ /Natica./ ]

The opercula have been utilized a great deal in the classification

of the /Gasteropoda/, and especially in some groups that have become

terrestrial in habit. Often, when shell-characters utterly fail to

give a clue to the proper generic position of a new or rare mollusk,

the operculum may be relied upon to indicate it.

[Illustration: Various forms of opercula. /Pyrula./ /Purpura./

/Littorina./ /Aulopoma./ /Torinia./ /Neritopsis./ /Strombus./

/Conus./]

TENTACLES

Two tentacles project like fleshy horns from the sides of the head.

These are not retractile, as in the land-snails, and their office

appears to be that of sensory organs. In both /Fulgur/ and /Buccinum/

the tentacles are comparatively short and stout, and have expanded

bases; in many other genera they are long and slender. Almost without

exception the /Gasteropoda/ possess tentacles. [pg333]

EYES

In /Fulgur/ the eyes are situated near the bases and upon the outer

sides of the tentacles; in /Buccinum/ they are extremely small and

are mounted about midway between the bases and the tips of the

tentacles. This is the usual position for the eyes in the marine

/Gasteropoda/. Only in the pulmonates, or land-snails, are the eyes

placed at the summit of the tentacles. Sight does not appear to be

a very important sense in the gasteropods, although the eye in some

instances becomes a highly developed organ. A number of forms that

have the habit of burrowing deep into the sand or mud are quite

destitute of visual organs, and certain cave-dwelling land-shells

have entirely lost the sense of vision.

MOUTH AND PROBOSCIS

The mouth will easily be seen in both /Fulgur/ and /Buccinum/. It is

a small slit with slightly thickened, fleshy lips, and is placed on

the lower forward portion of the head. In the case of both of these

genera the mouth is situated at the end of a proboscis. It will be

noted that /Fulgur/ has a comparatively long and stout proboscis, or

snout, which is not retractile. /Buccinum/ has a smaller one. It is

fairly safe to assume that all gasteropods that possess a proboscis

are carnivorous. This organ is greatly developed in some genera,

where it actually exceeds in length the rest of the animal. In such

instances, no doubt, the creature is enabled to reach the interior

portions of the shells of its victims and to devour every vestige

of their flesh, for the mouth is most conveniently placed just at

the end of this long, trunk-like organ. The genera which have no

proboscis are, almost without exception, vegetable feeders.

We must now remove the animal from its shell. It is well to boil

it first, for this does away with the annoying mucous secretion

that is freely exuded by glands in the foot when the creature is

roughly handled. Alcoholic specimens are apt to be much contracted

and hardened, and are therefore less satisfactory as subjects for

anatomical study. If it is not convenient to boil the [pg334]

specimen, break away the shell with a hammer, using care not to

lacerate the soft, fleshy portion within; when this is accomplished,

wash the animal carefully to remove the slimy exudation. Note the

"visceral hump," which is spiral, and which formerly occupied the

upper-whorl portion of the shell. The thin skin covering it is the

mantle, which below is greatly thickened and free, lying about the

foot like a heavy fleshy flap.

MANTLE

The mantle-edge in both of these examples is simple; that is to say,

it possesses no fringe of tentacles, nor is it supplemented by extra

processes, characters which mark many genera of marine /Gasteropoda/.

In /Fulgur/ and /Buccinum/ the mantle-edge does not protrude below

the edge of the shell; but in many genera, especially those which

possess smooth, glossy shells, like the cowries (/Cypræa/) and the

graceful /Oliva/, the mantle is proportionately very much larger. In

these two genera, when the animal is extended, as in crawling about

the sand, the mantle curves upward and incloses a large portion of

the shell itself. Indeed, in some genera the shell is almost entirely

concealed by this extension of the mantle (/Sigaretus/, /Natica/,

etc.).

When the shell is removed, the folding of the mantle which

constitutes the siphon can be plainly seen. The office of the siphon

has already been referred to, also the fact that the presence of a

siphon in the gasteropod mollusk may always be determined by merely

glancing at the shell alone, for a notch at the base of the aperture

indicates the place through which the siphon passed. In /Buccinum/

this is merely a notch, but in /Fulgur/ the siphonal canal of the

shell is much longer. Just why the long siphons of some mollusks

should be naked and exposed to danger, while others are so carefully

protected by elongated, portions of the shell, is a mystery, but

nature is full of such contradictions.

THE GASTEROPOD FOOT

The foot is long, broad, and flat on the under side, like a disk.

The variations in the gasteropod foot are almost infinite. [pg335]

In some of the species it is amazingly large and powerful, as

in /Polynices/ (/Natica/), and in most of the forms which live

along sandy beaches. These are sometimes provided in front with a

wedge-shaped process called the /propodium/, which serves admirably

as a plow to push aside the heavy wet sand through which the animal

forces its way. In /Nassa/, which is so common all along our coasts,

the foot has two terminal appendages or points behind.

[Illustration: /Sigaretus l[oe]vigatus/, showing excessive

development of the propodium (/pr./) and metapodium (/met./) in a

mollusk living in sand (the shell, which covers only the liver and

adjacent parts, has been removed): /l/, liver; /s. ap./, aperture of

proboscis, here deflected from the median line; /t/, /t/, tentacles;

/f/, foot.]

[Illustration: /Oliva textilina/ showing how the front part of the

foot (/f/) is developed into a sort of fender, the propodium (/pr./):

/e/, /e/, eyes; /m. ap./, front appendage of mantle; /m. ap.´/,

hinder appendage of mantle, folded into the suture when the animal is

at rest; /si./, siphon; /t/, /t/, tentacles.]

There is no single feature of mollusks more important than the foot,

for upon the many modifications of this organ the various molluscan

classes are founded. The name /Gasteropoda/ means "stomach-foot,"

the latter organ being merely a thickening of [pg336] the ventral

surface of the animal, giving to the creature, when active, the

appearance of crawling upon its stomach.

If a living gasteropod is placed in a jar of sea-water and left

undisturbed it will soon crawl up the side of the glass and thus

afford an excellent view of the extended under surface of its foot.

The majority of the gasteropods are lethargic and slow in movement,

but others will be found to be exceedingly lively and able to creep

up the sides of the jar and make their escape in a surprisingly short

time. Further modifications of the foot will be mentioned later.

THE MANTLE CAVITY

Now let us place the animal with the foot below and the head facing

us. The spiral visceral hump will point back and away from the

observer. The mantle covering the visceral portion is thin and

translucent like an ordinary skin, but at the base of the visceral

mass the mantle suddenly thickens very greatly, and spreads over

the dorsal portion of the foot or the body like a cloak. The space

between the body and the loose-lying mantle is called the /mantle

cavity/, and within this area are to be found several important

external organs. To find these it is well to cut the mantle flap in

a straight line, beginning just back of the head and ending at the

point where the mantle is attached to the body. This will most easily

be done with scissors. Having thus divided the mantle in front, throw

back the two flaps. On the right-hand side (left of the animal), and

attached to the inner side of the mantle thus exposed, will be seen

the branchiæ, or gills.

THE BRANCHIÆ, OR GILLS

They consist of a row of flattened filaments bound together at the

base like the leaves of a book. The blood is conveyed to these

gills by a large vein, and is then forced through the thinly walled

filaments, being thus brought into close contact with the water, to

which it releases its carbon dioxide, and from which it receives the

life-giving oxygen. In certain gasteropods there are two sets of

gills, one placed upon each side of the body [pg338] (as in the

ideal mollusk); but the presence of two sets of gills only indicates,

in these gasteropods, that the twisting process of the viscera,

already alluded to as so remarkable a feature of this class, has not

proceeded far enough to destroy the functional activity of one of the

gills.

[Illustration: Anatomy of the internal organs of a female gasteropod,

viewed from the dorsal side. The roof of the mantle cavity has been

divided by a longitudinal incision and the flaps laid out, that on

the left bearing the ctenidium and osphradium, and that on the right

the rectum and terminal part of the oviduct. The muscular dorsal wall

of the body and the introvert have been divided so as to bring into

view the anterior part of the alimentary canal and a portion of the

nervous system. The buccal cavity has been tilted up and opened so

as to show the odontophore, and the esophagus has been cut through

near the anterior end. A portion of the ventral wall of the crop

has been removed so as to bring the internal folds into view, and

the interior of the nephridium with the contained portion of the

intestine has been exposed. The stomach is not seen, being hidden by

the nephridium, and the ovary is not represented. /an./, anus; /ant.

aort./, anterior aorta; /aur./, auricle; /buc./, buccal cavity; /cer.

buc. con./, cerebro-buccal connective; /cer. g./, cerebral ganglia;

/crop/, crop; /cten./, ctenidium; /int./, intestine; /jaw/, jaw;

/l. buc. g./, left buccal ganglion; /l. sal. gl./, left salivary

gland; /neph./, nephridium; /neph. ap./, nephridial aperture; /od./,

odontophore; /oes./, esophagus; /oes'./, anterior end of same, cut

and turned aside; /osph./, osphradium; /ovid./, oviduct; /ovid'./,

terminal thick-walled portion of oviduct; /pleur. g./, pleural

ganglion; /post. aort./, posterior aorta; /post. oes./, posterior

esophagus; /rad. s./, radula sac; /r. sal. gl./, right salivary

gland; /rect./, rectum; /sal. du./, salivary duct; /siph./, siphon;

/supra. g./, supra-esophageal visceral ganglion; /tent./, tentacle;

/vent./, ventricle.]

In general, it may be said that the breathing process of mollusks

does not markedly differ from the respiratory methods of higher

forms of animals. Whether the breathing is effected by gills or by

a pulmonary sac, the essential features of the system are the same

as in fishes or mammals. There are, however, some rather peculiar

developments in the breathing system of gasteropods that are worthy

of notice. The gills themselves differ throughout the various orders

of this class both as to their structure and their relative position;

in one of the orders (the /Pulmonata/) the gills have entirely

disappeared, and are replaced by a pulmonary sac which fulfils the

purpose of a lung.

It is a generally accepted theory that all land or air-breathing

mollusks were originally marine, but by a gradual change in their

habits have developed into terrestrial forms, losing their gills

and acquiring in their place organs which correspond to lungs. The

theory is supported by the fact that many species of marine mollusks

live between tide-marks, and for several hours daily are obliged to

maintain life outside of their native element. The /Littorinidæ/,

which may always be found in abundance on both the east and the west

American coasts, usually live high above low-tide line, and some

tropical species of this genus actually live in the trees above

the reach of high tide. They have gills just as in /Buccinum/ or

/Fulgur/, but the /Littorina/ shell is strongly suggestive of certain

land forms, and there is reason to believe that the genus is in

course of evolution into a pulmonate. On the other hand, there are to

be found in fresh water numerous genera which are true pulmonates,

and which are obliged to come to the surface every few minutes to

obtain air. One notable genus of marine gasteropods possesses both

lungs and gills, and one marine form has entirely lost its gills

and breathes only by means of lungs. It is quite likely that all

mollusks are able to breathe more or less all along the exposed

mantle surface, which is usually [pg339] crowded with capillaries

with exceedingly thin walls. This very remarkable method of surface

respiration is proved to exist in the nudibranch or shell-less marine

/Gasteropoda/, for they possess neither gills nor lungs.

OSPHRADIUM

Lying just under the gills, and side by side with them, is a smaller,

plume-like organ having the appearance of a smaller gill; it is

called the /osphradium/. The office of this organ is not definitely

known, but the supposition is that it is the seat of the olfactory

nerves. The osphradia are not always present, but whenever found they

are placed in close conjunction with the gills, in order, probably,

that the animal may best determine the quality of the water brought

by the siphon to the breathing-organs. In /Buccinum/ the osphradium

is especially prominent. In all mollusks the sense of smell is highly

developed. A dead animal anchored to the bottom will very soon

attract the carnivorous /Mollusca/ from every direction. This is not

a bad way to trap certain species that live upon rocky stations and

are otherwise difficult to secure by the dredge.

On the left-hand side (right of the animal), and adhering to the

under side of the mantle flap, which has been thrown back, a somewhat

inflated and convoluted tube, the rectum, will be seen. It terminates

in an opening just within the mantle-edge. By the side of this are

the renal and genital openings.

* * * * *

Having now examined the external organs, we may investigate the

internal anatomy of our subject. To do this thoroughly requires

considerable skill, but for the purpose of merely discovering the

relative positions of the principal internal organs a little care

only is necessary. The work will be greatly facilitated by boiling

the animal for a few minutes, for this serves to harden the tissues

and to separate the various organs in a most satisfactory manner.

To begin, open the proboscis from the mouth, cutting back so as to

expose the esophagus. It will be seen that the throat is long and

very muscular. [pg340]

RADULA

Hidden among the red stripes of muscular fiber which line the inner

surface of the throat will be found a fleshy strip covered upon

one side with many transverse rows of chitinous teeth. This is the

/lingual ribbon/, or /radula/. Remove as much of it as possible, and

examine it with a hand-glass. The radula is a most important organ,

and is a unique possession of /Mollusca/, except the pelecypods, or

bivalves. Usually it lies coiled up like a spiral when not in use;

its purpose is to tear and rasp food.

[Illustration: Three rows of teeth from the radula of /Fasciolaria

trapezium/.]

[Illustration: Portion of the radula of /Imbricaria marmorata/.]

The radula has been the subject of much study by conchologists, and

has furnished the basis for an arrangement of the numerous sections

of gasteropods into somewhat well-defined groups. If the observer has

a strong glass he will notice that each transverse row of teeth on

the ribbon consists of a median or central tooth with several points

or "cusps." /Fulgur/ has a median tooth with three cusps; /Buccinum/

one with six. On each side of the median tooth is a lateral tooth,

which in /Fulgur/ will be seen to have six cusps, and in /Buccinum/

five. In many patterns of radulæ there is, besides the median and

lateral teeth, still another paired row, called the marginals. In

the accompanying figures are given some examples which show small

sections of lingual ribbons. While all the radulæ of mollusks are

capable of being grouped by their general characteristics, yet in no

two species of mollusks are the radulæ quite identical. [pg341]

VITAL ORGANS, STOMACH, LIVER, RENAL GLANDS, ETC.

The digestive tract will be found to widen out a short distance back

into a crop or stomach, and, continuing still further, to lose itself

in a soft, brownish mass within the coiled spire, which is the liver.

The very large size of the liver leads one to suspect that /Fulgur/

and /Buccinum/ must be voracious creatures to need so large an organ

for the secretion of bile. In many species of mollusks the stomach

and intestines are filled quite solidly, at times, with a gelatinous

transparent substance called the /crystalline stylet/. Just why the

digestive tract should be clogged with this substance no one has

yet been able to explain, so here again is a chance for original

investigation. The intestine curves about after reaching the liver,

and comes forward again to appear once more as the rectum, clinging

to the inner surface of the free portion of the mantle.

Closely associated with the liver, but differing slightly in color,

is the gonad, or organ in which the genital products are formed.

Situated dorsally and forward of the liver and gonad is a large renal

gland, which may readily be detected by its peculiar structure. In

some forms the kidney is closely associated with the gonad, and seems

to coöperate with the latter in the generative functions.

HEART AND VASCULAR SYSTEM

To find the heart, make an incision into the body just at the

posterior end of the gills. The heart is white and round, and

is inclosed within a cavity known as the /pericardium/; it has

a ventricle and one or two auricles, although in /Buccinum/ and

/Fulgur/ there is but one auricle.

There is nothing remarkable about the vascular system to distinguish

it from that of many higher forms of animals. It is, however, not

completely closed--by which is meant that the blood is not always

contained within arteries or veins, and that it does sometimes flow

into other organs and floods certain other body-cavities, although

the vascular system of mollusks is by no means so completely open as

is that of insects and crustaceans. [pg342]

Having examined the animal which inhabits the shell and gained an

idea of its anatomy, we may now turn to an inspection of the house

which it has built for itself, and here we shall find a delightful

subject for study.

THE GASTEROPOD SHELL

An industrious hour of collecting upon almost any beach will provide

the student with an abundance of interesting shells. Putting aside

the bivalves, the univalve or gasteropod shells remaining should be

closely examined for the purpose of becoming acquainted with their

various conchological features. The collector will see at once that

he has a number of species that differ more or less widely in their

general form, size, texture, and sculpture. Some shells will be long

in proportion to their width, with many turns of the spire which

probably terminates in a sharply pointed apex; others will be almost

round, with comparatively few spiral turns which end in a blunt apex,

giving to the specimen outlines suggestive of a dome. A wide range of

characters will be found in the mouths or apertures of the shells,

some being almost if not quite round, others oblong and with a notch

cut into the lower portion of the opening, and others possibly with

this notch extended into a sort of semi-inclosed channel. A first

lesson in classification of the /Mollusca/ may be taken by dividing

the results of the first day's collecting of univalve shells into

groups according to these prominent shell-characters.

[Illustration: Parts of a gasteropod shell: /a/, anterior canal; /b/,

body-whorl; /c/, columella; /l/, outer lip; /m/, mouth or aperture;

/p/, posterior canal; /s/, sutures; /sp/, spire; /u/, umbilicus.]

A good knowledge of the parts of a gasteropod shell is essential to

the student, and it can readily be acquired. Four specimens are given

in the accompanying figures, representing highly divergent [pg343]

types of marine gasteropods, and their respective characteristics may

be noted by comparing them one with another: /Fasciolaria tulipa/

(Plate LXXVI.), a Floridian shell; /Polynices heros/, a common

species found on all the sandy shores of the American Atlantic

coast; /Murex tenuispina/, an Indo-Pacific species much prized by

collectors; and /Acmæa testudinalis/, commonly found in Maine and

Massachusetts at low tide clinging to rocks.

[Illustration: /Polynices heros/; /Acmæa testudinalis/, from below;

/Acmæa testudinalis/, profile; /Murex tenuispina/.]

The extreme top of the shell is called the /apex/, and it may be

either sharply pointed or obtuse. Each turn is called a /whorl/; the

last one, and always the largest, is called the /body-whorl/, the

others collectively forming the /spire/ of the shell. When the animal

first emerges from the egg it is always provided with one or two

whorls, which generally may be distinguished at the apex as smoother

than the rest of the spire, and a faint line may be discovered where

the shell began its growth after birth. These [pg344] first whorls

of embryonic growth are usually referred to as the /nepionic whorls/.

The interstices between the successive whorls are called /sutures/,

and these lines of juncture may be shallow or deep according to the

convexity of the whorls. The sculpturing of the whorls is often

of great complexity, and exhibits /nodules/, /varices/, /ribs/,

/revolving striæ/, /spinous processes/, and /lines of growth/.

It frequently happens that there is a complete absence of any

sculpturing whatever, the whole surface of the shell being perfectly

smooth, save for the faint lines of growth to be detected only under

a magnifying-glass. The outer edge of the mouth or aperture of the

shell is called the /outer lip/. This may be more or less thickened,

expanded, or simple. The inner lip is called the /columella/, and may

be greatly extended anteriorly. When the mouth of the shell is round,

and there is no notch or indentation either above or below, it is

said to be /continuous/.

The /anterior canal/ is for the accommodation of the siphon of the

animal, which, as noted above, may be very long or almost entirely

absent; therefore the character of the shell generally indicates

whether or not the animal itself possesses a long siphon. There is in

some forms a notch at the upper extremity of the mouth, which is for

the accommodation of the anal discharges. When present it is called

the /posterior canal/.

It will be noted that all the specimens figured as examples, save

one, are spiral, the coils revolving about an imaginary axis. When

the whorls are not too closely coiled there is left open to the view

a hollow space throughout the entire length of the shell, which is

called the /umbilicus/. When the coils of the shell are very compact

there is no umbilicus to be seen. The umbilical opening may be very

large, giving a clear view of the inner surfaces of all the whorls

right through to the apex. The usual gasteropod shell is in reality a

hollow tube wound about an imaginary axis. Since the tube increases

in size as it progresses, the base of the shell is necessarily

wider and larger than the apex. Thus all gasteropod shells may be

reduced in shape to the single type of a cone or top, modified by

the excessive length or shortness of the spire, or otherwise altered

by special peculiarities. In /Polynices duplicata/ (page 368), it

will be observed that while the [pg345] umbilicus is fairly large,

its external opening, in the adult shell, has been almost completely

closed by a callous process thrown off from the inner or columellar

lip.

Gasteropod shells may be /sinistral/ or /dextral/, according as

the whorls turn to the left or right. The great majority of marine

species are dextral, having the opening on the right, although a

few species exhibit the curious property of being constructed upon

either the one or the other plan without apparent reason. Sinistral

specimens of many normally dextral species have been discovered, but

they are so rare as to warrant the belief that such specimens are

merely deformities or monstrosities resulting from some accident of

birth.

The collector will soon learn to distinguish between young and adult

specimens, for those finishing touches of wonder and beauty which

the mollusk gives to his protective covering are made only by the

adult. The outer lip of young gasteropod shells is usually thin and

fragile; even if slightly thickened, it has an unformed or unfinished

appearance.

Shells differ greatly in their /structure/, many species being

porcelanous like china, others glassy, and many more are of a softer

chalky composition. In the latter case the shell is usually covered

with a thick membranous skin, which, when removed, leaves a dull,

lusterless, white body beneath. Shells of this texture, when cast

upon the beach, soon yield to the weathering action of sun and air.

The porcelanous shells are composed of successive layers of carbonate

of lime, throughout which is a filmy membranous framework of a

substance similar to that of which the covering of the /Crustacea/ is

formed. The mode of deposition of the various layers of crystalline

calcic carbonate and the peculiar lineation of their outer surfaces

give rise to the iridescent or nacreous appearance of some shells.

With the exception of those species in which the mantle of the

animal is extended over the edge of the aperture and more or less

envelops the entire test, there is an outer skin of membranous or

organic matter which overlies the surface of the shell. This skin

is sometimes quite thick, often hairy, and is usually of a dull

greenish- or brownish-yellow color. In many genera this [pg346]

outer covering of the shell is excessively thin. In old specimens

the epidermis is usually worn away from the apical whorls. It often

happens that the shells of the most exquisite colors and markings are

thus rendered somber and unattractive by their tenants during life;

when the animal dies, or when such specimens are kept in a cabinet

for a period of time, the epidermis dries, cracks, and falls off,

revealing the wealth of color and design beneath.

The growth of the gasteropod shell is accomplished by the exudation

from the margin of the animal's mantle of a liquid containing the

shelly matter in solution. The mantle-edge is provided with a

complicated system of glands and pores, from which is secreted this

"stony liquor." This more or less viscous liquid, containing the

carbonate of lime and the other inorganic materials of which the

shell is composed, hardens upon exposure, and the shelly matter is

then deposited in crystalline form around the edges or lip of the

shell aperture. The gasteropod shell therefore grows by the continual

building out of its aperture through successive depositions of shelly

matter at the extreme edge of the lip. At the extreme edge of the

mantle margin are situated those glands which secrete the materials

for the epidermis of the shell, and as one would therefore expect,

this outermost layer of epidermis is first produced in the advancing

growth of the shell. There also are situated the pigment-glands,

which produce the color-secretions. The various layers of the shelly

substance are successively deposited inside the mouth of the shell by

glands situated just back of the extreme edge of the mantle margin.

Thus in the growth stage, if one could examine closely the aperture

of a gasteropod shell, one would observe at the extreme tip of the

lip this projecting epidermis, just beneath it and just inside the

aperture a thin deposit of shelly matter, just beneath this, and

farther in, another layer, and still farther in a third layer.

The growth of nearly all gasteropod shells is marked by periods of

rest. During the inactive seasons the creature may thicken the edge

of the aperture to a greater or less extent by an extra deposit of

shelly matter, for otherwise the thin lip might soon be [pg347]

injured or broken. These places where the lip was thickened, as a

temporary protection until the young animal decided to continue

building, appear on the surface of adult shells, and persist as

/varices/, "raised lines of growth," "longitudinal ribs," etc. Such

forms of sculptural markings generally occur at equidistant points

and preserve a scheme of regularity which would indicate that the

periods of rest were of seasonal occurrence. All irregularities and

all surface features of the external shell simply reflect certain

peculiarities of the mantle margin of the animal; all spinous

processes, for instance, as in the marvelous /Murex tenuispina/,

indicate the existence of finger-like processes extending from the

mantle margin, which once occupied the hollow thorns projecting

from the shell. When the outer surface of a shell is devoid of

any sculpturing and is perfectly smooth, one may assume that the

mantle margin of the animal was simple. If the edge of the lip has

a crenulated appearance and the surface of the whorls is decorated

with revolving ribs, the mantle margin was probably folded or wavy.

There can be no doubt but that the entire mantle surface is provided

to some extent with glands for the secretion of shelly matter, for

if any portion of the shell is accidentally injured the animal soon

repairs the break with a calcareous deposit. But such repairs are

never homogeneous in texture with the other parts of the shell of

normal growth; the patches are never covered externally with an

epidermis, and they are always devoid of color. The function of the

epidermis is to protect the calcareous shell from the corroding

agents contained in sea-water. Hence it is that, when the epidermis

is removed, "dead shells" exposed to the influence of the water

or the weather soon lose their brilliancy and luster, and become

undesirable for specimens either for the cabinet or for study. It

often happens that living shells, inhabiting a region where, for one

cause or another, the water is highly charged with impurities of an

acid nature, are discovered to be badly corroded about the apex,

where the epidermis is thin and likely to be rubbed off. For this

reason specimens collected in harbors near large cities or near the

mouths of rivers are apt to be poor and defective.

The inner surface of all shells, if not actually nacreous, is

[pg348] always perfectly smooth. When foreign substances, such as

grains of sand, enter the shell and cannot be removed by the animal,

the irritation caused thereby to the soft, fleshy creature induces

discharges of a liquid from the glandular surface of the mantle,

which hardens about the offending substance and glazes it over with a

smooth, pearly deposit.

/Acmæa testudinalis/ (page 343) presents a special type of gasteropod

shell which is found in several families. Here the spire seems to

be wholly absent, and the entire shell consists of but one large

body-whorl. There are very many of these patelliform species,

inhabiting many seas and belonging to many different genera, and

in nearly all cases their embryonic shells display a spiral form.

After birth the animal does not build his house upon the spiral

plan, but expands the shell into one large shield-like covering.

The student, however, must not presume that /Acmæa/ is an ancestral

type just because the simple character of the shell is suggestive

of the model chosen to represent a schematic mollusk; anatomically

/Acmæa/ presents the complications of body-torsion which show a very

considerable evolutionary change, and indicate that its simple shell

is probably a degenerate form of a once more highly developed and

convoluted one.

The forms, the architecture, and the painting of gasteropod shells

are so infinite in variety that it would be unwise to attempt a

description of their marvels. A close observer of nature's works

soon becomes prepared for every surprise, but he never ceases to be

charmed and fascinated by his new discoveries. The careful student

alone can learn really to see and appreciate the wonders of nature,

and this is especially true in the study of the /Mollusca/.

CLASSIFICATION OF GASTEROPODS

The /Gasteropoda/ far exceed all the other divisions of the

/Mollusca/ in the number of their genera and species. Apparently

this has not always been the case. There is evidence tending to show

that in past geological epochs the pelecypods (the bivalve shells)

outnumbered the gasteropods, but that in the course of time the

increase in the genera of gasteropods has been more [pg349] rapid.

To judge also from the very large number of extinct families among

the cephalopods, which once flourished in astonishing abundance, it

would appear that they are a dying race.

The classification of the /Gasteropoda/ is primarily a division into

three great orders: the /Opisthobranchiata/, the /Prosobranchiata/,

and the /Pulmonata/. The /Pulmonata/, which include the land and

fresh-water gasteropod shells, are characterized by the presence of

a breathing-sac, or lung, instead of gills. They are, therefore,

essentially air-breathers, and would perish if kept too long under

water. The /Opisthobranchiata/ and /Prosobranchiata/ are marine,

and, like all animals which breathe by means of gills, soon die

when removed from the water. We have already noted, however, how

some genera of marine gasteropods that find their station about

high-tide mark are able to live for considerable periods out of the

water, notwithstanding the fact that they are fully equipped with

gills and not possessed of lungs. Indeed, there is one large family

of prosobranchs (the /Cyclostomatidæ/) that has become entirely

terrestrial in habit, its members having lost their gills and

acquired lungs, but their organization otherwise is so essentially

that of the prosobranchs that they have never been considered as

pulmonates.

The main difference between these two orders of marine gasteropods

is that in the prosobranchs the breathing-organs (the gills) are

placed in a position forward of the heart, and the degree of torsion

(page 330) characteristic of this molluscan class has been continued

until the auricle of the heart is in front of the ventricle. There

is always a shell, usually spiral, and, with few exceptions, an

operculum. In the opisthobranchs, on the other hand, the relative

position of the heart and gills is reversed, and they further differ

from the prosobranchs in that the sexes are always united in each

individual. The opisthobranchs are not always provided with a shell.

One division of the order, known as the "nudibranchs," are entirely

naked. These are commonly called the "sea-slugs," and are to be

found crawling about the marine vegetation in shallow water, in

tide-pools, and on the piling of old docks. Curiously enough, the

sea-slugs (see page 354) have no gills at all, but, having lost these

apparently essential organs, are [pg350] enabled to "breathe water"

through their skin. They are wonderfully beautiful creatures, and the

collector must not fail to secure some specimens, put them into a jar

of sea-water, and watch them expand.

There are other more superficial differences between the prosobranchs

and the opisthobranchs, which will enable even a beginner to

distinguish them at a glance. When the latter are possessed of an

external shell, it is bulbous, generally glassy, and with a simple

lip, the aperture extending the entire length of the shell. Again,

the mantle or the propodium of the foot is greatly extended and

usually covers the shell almost wholly.

With the exception of the nudibranchs, which are common all along

the Atlantic shore, especially north of Cape Cod, there are very few

opisthobranchs to be found in American waters. Their shells are not

very abundantly found anywhere, though in Florida there are two or

three species which an untrained collector might discover.

Practically all the gasteropod or univalve shells that will be taken

by the ordinarily expert collector along the shore are prosobranchs.

This order includes the great majority of marine gasteropods, and

is entitled to the distinction of claiming, in the great number of

its genera and species, the most startling eccentricities of form

and color to be found among the /Mollusca/, if not among all marine

invertebrates.

Only those species which are actually abundant on the Atlantic and

Pacific shores of the United States, and which are likely to be found

by the untrained collector, are selected from the long list of forms

which belong to the three faunal regions involved.

ORDER =OPISTHOBRANCHIATA=

SUBORDER ~TECTIBRANCHIATA~

To avoid confusion, it is well to keep the systematic table in view:

Class Orders Suborders

=GASTEROPODA= =OPISTHOBRANCHIATA= =TECTIBRANCHIATA=

=NUDIBRANCHIATA=

=PROSOBRANCHIATA=

=PULMONATA=

[Illustration: PLATE LXV. Bulla occidentalis, enlarged. Bulla

nebulosa. Lottia gigantea, inside view. Fissurella alternata.]

As has already been remarked, shell-bearing opisthobranchs are not

abundantly represented in number of species in North American waters.

South of Cape Cod, in muddy bays and well-sheltered places, the

little shell, /Haminea solitaria/, may, however, often be found in

considerable numbers.

GENUS ^Haminea^

^H. solitaria.^ Like all external opisthobranch tests, the shell of

this species is thin and fragile, and would appear to be of small

importance to the creature it only partially protects. It is devoid

of spire, is shining bluish-white, sometimes brownish in color,

and is marked with revolving grooves, which, being cut across by

irregular growth-lines, give its surface a faintly decussated

appearance. The aperture is as long as the shell; the columella is

incurved. This little species is especially abundant in shallow

water about Vineyard Sound and in Peconic Bay.

[Illustration: /Haminea solitaria./]

GENUS ^Bulla^

^B. occidentalis.^ This species, which is found in the waters

of Florida on all sandy beaches, is a relative of the Northern

species just described. The shell is larger than that of /Haminea

solitaria/, and has a color-pattern of mottled or clouded

reddish-brown on a white foundation. There is no spire; there

is a pit in place of an apex; and the aperture extends the full

length of the shell. To the naked eye the surface appears smooth

and shining. It is an exceedingly variable species, occurring all

through the West Indies, but not north of Florida. The shores of

the keys along the west coast of Florida are often strewn with

these shells after storms. The animal, like all the shell-bearing

opisthobranchs, is very large as compared with the shell, and the

large mantle folds recurve upward, almost completely hiding the

shell from view. (Plate LXV.)

^B. nebulosa.^ This is one of the largest and finest species of

the family /Bullidæ/. It is found on the coast of California south

of San Francisco. The shell is much larger than that of either of

the Atlantic species mentioned above, but very closely resembles

them in outline, although it is built upon a more generous plan

and is more richly painted. It is brownish, mottled with white and

yellow patches, and is very suggestive of certain kinds of birds'

eggs. The animals have a greatly extended mantle which almost

completely envelops the shell. The foot is extremely large, with

great wing-like developments upon each side, called parapodia. Some

species of /Bulla/ have been seen to swim by means of the lazy

flapping of the parapodia. (Plate LXV.)

SEA-HARES

Closely allied to these outer-shell-bearing opisthobranchs is a large

and important group of tectibranchs, known as [pg351] "sea-hares."

They have a mantle so greatly developed that it actually covers the

shell, and its edges unite and fuse over the top. The shell, in

consequence, having almost ceased to be of use as a protection, has

degenerated into a mere horny plate, and has lost all resemblance to

the ordinary gasteropod shell. Having practically lost its protective

office and become a mere internal plate, it is quite probable that

it will in time wholly disappear. The gills of the sea-hares are

concealed under a flap of the mantle, their position being posterior

to the heart. The most conspicuous representative of this type of

tectibranchs in the United States is the following:

GENUS ^Aplysia^

^A. Wilcoxii.^ This species appears at times in vast numbers in

the waters of Florida, until the sea may truly be said to be

fairly alive with them. They swim lazily with a waving motion of

the parapodia. They disappear as mysteriously as they come, and

for months not a specimen will be seen. There is a variety of this

Floridian /Aplysia/ which occurs at Cape May, but no sea-hares are

to be found north of that point. The tropical Pacific furnishes an

astonishing wealth of these creatures, belonging to many genera

and species, and among them are some of the most beautiful of the

invertebrate animals.

SUBORDER ~NUDIBRANCHIATA~

The opisthobranchs are divided into two suborders, the second of

which is called /Nudibranchiata/. The name is well chosen and

very suggestive, for it means "naked or exposed gills"; but this

anatomical feature is only one of the peculiarities of this suborder.

The nudibranchs are commonly known as "sea-slugs"; for, like the

land-slugs, which are also true mollusks, they possess no shell at

all. That they at one time carried a shell is evident from the fact

that they are born with a rudimentary testaceous covering, which soon

afterward disappears.

A striking peculiarity of the nudibranchs is that the conventional

molluscan mantle is not usually apparent. Instead of seeing the usual

flaps or folds of the mantle which more or less encircle mollusks,

and which one seems to have a right to expect, [pg352] they are

entirely absent, and the body of the sea-slug assumes in consequence

a worm-like appearance. Other notable features of the nudibranchs

are the great number of tentacular processes that usually project

from the dorsal region of the animal, and, in many of the genera, an

entire absence of gills. When the gills are present, as is the case

in several of the nudibranch families, they are not placed along the

side of the animal, where one would naturally look for them, but are

arranged in the form of a rosette of plume-like processes situated in

the posterior dorsal region, or, in other words, on the animal's back.

Nudibranchs are commonly to be found all along the Atlantic and

Pacific coasts of North America, and more especially in the colder

waters north of Cape Cod. They are essentially littoral, and live

upon algæ in shallow water, upon eel-grass in sheltered places,

and in tide-pools, where there is more or less vegetation. They

crawl about the fronds of algæ, or swim, foot upward, with a gentle

and undulating motion, or, when caught between tides, may be seen

clinging to the under surface of rocks. Protective resemblances

have been so remarkably developed in the nudibranchs that they are

not always easy to discover; indeed, one may actually be looking at

one for some time without suspecting it to be other than some torn

fragment of seaweed.

* * * * *

There are many species belonging to several genera which frequent

the Maine and Massachusetts coasts, but those most likely to be

encountered are the following:

GENUS ^Dendronotus^

^D. arborescens.^ This species is about one inch long and variable

in color, but is usually reddish-brown or rose. There are no

tentacles, but in their place are two antler-like appendages

pointing forward and branched like a tree. All along the back are

two rows of these curiously branched processes, which give to

the animal the appearance of a plant. These /cerata/, or dorsal

papillæ, are delicately transparent, contractile, and richly

colored. The function of these papillæ is not fully known. As

the animal has no specialized breathing-organs, it is reasonable

to suppose that respiration is carried on through the outer skin

and perhaps all over the surface of these branched papillæ. The

liver, which [pg354] in most nudibranchs is extremely large and

completely surrounds the stomach, in /Dendronotus/ also extends

into these dorsal cerata, so that they may have some sort of

digestive function.

[Illustration: /Dendronotus arborescens./]

GENUS ^Æolis^

^Æ. papillosa.^ This is probably the commonest nudibranch upon

the North Atlantic coast, and it occurs as frequently in European

waters. It may readily be found clinging to stones, algæ, the

piling of wharves, eel-grass, etc., in bays or in rocky tide-pools.

The color is yellowish-gray to orange, with purplish or olive

spots. The cerata are very numerous, and cover the dorsal portion

of the animal save for an open space along the middle of the back.

There are two sets of tentacles, the two dorsal and the two simple

labial tentacles. The foot tapers behind to a sharp point, and is

truncate in front. As in /Dendronotus/, the liver is diffused into

the cerata, which in /Æolis/ are simple tubular processes without

the branching character of those of the former. Both species lay

their eggs in a gelatinous, bobbin-like cord, which is hung in

festoons over rocks or upon zoöphytes, or at times they wind the

cord in a coil upon the surfaces of stones. When the young first

hatch out, they are provided with a glassy nautiloid shell, a fact

which would indicate that at some remote period they were, like

most mollusks, provided with a shell. /Æolis/ swims in an inverted

position, and is at times exceedingly active. It is very variable

in coloring and in the number of cerata.

[Illustration: /Æolis papillosa./]

GENUS ^Doris^

^D. bilamellata.^ In /Doris/ we find a quite different type of

nudibranch from that presented by the two genera /Dendronotus/

and /Æolis/. In one there were numerous branched cerata or dorsal

papillæ, in the other many plain cerata, and in neither case were

there any specialized [pg355] breathing-organs. In /Doris/,

however, there are no dorsal papillæ at all, the back being covered

with calcareous spicules, which form a sort of secondary shell.

There is a circlet, or rosette, of retractile plume-like gills, or

branchiæ, placed in the middle of the back posteriorly. There are

various species of /Doris/, and of closely allied genera belonging

to the family /Dorididæ/, which are to be found along the New

England coast in tide-pools and among rocks. Those seen by the

writer never appeared to be other than very sluggish creatures, and

proved to be rather unsatisfactory tenants of the aquarium.

[Illustration: /Doris bilamellata./]

When discovered at low tide upon moist seaweed or stones, or when

disturbed in the water, nudibranchs often appear like small lumps of

jelly-like tissue, without a single attractive feature. It is only

when they are placed in a jar of sea-water and left unmolested for

a few moments that they unfold their beauties to the view. On the

Pacific coast there are numerous species of nudibranchs, occupying

corresponding shore stations and exhibiting the same degree of high

coloration. There are over a thousand species of sea-slugs scattered

about the various seas. They find their greatest development in

tropical waters, and for brilliancy of tint and variation in form

are unequaled by any other class of animal life, save perhaps the

butterflies.

ORDER =PROSOBRANCHIATA=

To this exceedingly large and comprehensive order of gasteropods

belong the great majority of univalve mollusks. In point of number of

genera and species and in abundance of individuals, the prosobranchs

probably exceed all the other orders of mollusks combined. They may

be called the typical gasteropods, the shell being univalvular and

generally spiral, and the animal exhibiting the singular torsion

of the visceral mass which has placed the breathing-organs forward

of the heart. They are provided with an operculum (placed upon the

posterior dorsal portion of the foot), which is used to close the

aperture of the shell against [pg356] enemies when the animal

retires within its fortress. They are all marine except a very

few families, which, supposedly of marine derivation, have become

terrestrial in habit.

The prosobranchs are further subdivided into suborders according to

certain peculiarities of the heart and breathing-organs. There is

a group of these prosobranchs which gives evidence of an inferior

degree of that visceral torsion which is always found in the

gasteropods. In this group, or suborder, the heart has two auricles,

and there is a pair of gills instead of only a single one. Other

internal organs are paired just as they were represented to be in

the schematic mollusk. This group also seems to show its primitive

character in the want of a proboscis and a siphon, or, in some

families, by having the ventricle of the heart traversed by the

intestinal canal, just as in the lower class of mollusks, which

includes the clams and oysters. For the most part the shells of this

group are not typically spiral, but are patelliform, shield-like

coverings, with only a suggestion of a spiral form at the very tip

of the apex. This group of primitive prosobranchs is included in the

following suborder:

SUBORDER ~DIATOCARDIA~

This suborder is named from the presence of two auricles in the heart.

FAMILY ~ACMÆIDÆ~

The first family to be noted is the /Acmæidæ/. Its principal genus,

/Acmæa/, is well represented on both the east and the west coast of

the United States.

GENUS ^Acmæa^

^A. testudinalis.^ This species is found in vast numbers all along

the New England shore, clinging to the rocks between tides. They

are usually called limpets. The shell is solid, conical, with an

oval outline, and with no trace of a spiral form in the adult. When

the shell is thoroughly cleaned, it generally presents a mottled

coloration of pale green, brown, and white. Inside it is white

and nacreous, with a large brown [pg357] area under the apex.

The animal has a powerful foot, by means of which it is enabled

to cling to a rock with great strength. In order to dislodge it,

it is necessary to approach carefully, and, taking the creature

unawares, quickly slip a broad knife-blade under the foot,

otherwise it is quite impossible to tear it from its resting-place.

/A. testudinalis/ lives entirely between tides, and ranges from the

northernmost waters to New York. It feeds upon algæ and is a very

sluggish animal. It has been said to leave its resting-place and

wander about in search of food, returning to its original and usual

spot when the tide begins to ebb. (Page 343.)

^A. testudinalis,^ variety ^alveus.^ This variety is smaller, more

fragile, and oblong. It lives upon eel-grass, its oblong shell

being adapted to the narrow leaves of the grass. The coloration is

brighter--reddish-brown spots on a white surface. It is exceedingly

common on the New England coast.

[Illustration: /Acmæa testudinalis/, var. /alveus./]

^A. mitra.^ On the Pacific coast there are a number of acmæas. /A.

mitra/ is often found dead upon the beaches. It is conical in form

and pure creamy-white in color. It looks very much like a clown's

pointed cap.

^A. patina.^ This is also very abundant in California. Outside it

is dark in color and is often incrusted with mineral deposits.

Within there is a dark ring around the edge, then a zone of

bluish-white, and a patch of brown just beneath the apex.

GENUS ^Lottia^

^L. gigantea.^ This is the largest of the California limpets.

Specimens three inches long have been found. The outer surface

of the shell is rough and brownish in color. The apex is near

one end. Within it is almost black, shining, lustrous, with a

horseshoe-shaped muscle-scar under the apex. The color is bluish

and brown. (Plate LXV.)

FAMILY ~FISSURELLIDÆ~

This is an extensive family, including several genera and a number

of species, commonly known as keyhole-limpets. In the general form

of the shell they closely resemble the true limpets, the /Acmæidæ/,

except that they have a hole, or rather a slit, in the shell just

back of the apex. Often this slit is so long that it has entirely

removed the apex of the conical shell.

GENUS ^Fissurella^

^F. alternata^, ^F. barbadensis^. These species occur upon the

southern shores of the United States, the latter, however, being

confined to [pg358] extreme southern Florida. /F. barbadensis/

has heavy longitudinal ribs and is light green within, with a rosy

circle about the apical perforation. (Plate LXV.)

GENUS ^Glyphis^

^G. aspersa.^ One of the numerous species belonging to this family

which are found on the west coast of the United States. It is about

one and a half inches long, grayish-white, with sharply raised

longitudinal ridges, slightly rayed, crossed by revolving ribs,

which give to the outer surface a decussated appearance. The apex

is forward of the center, and is entirely replaced by a round

perforation. The edge is wrinkled, and within smooth and white.

GENUS ^Lucapina^

^L. crenulata.^ The largest of the keyhole-limpets; the shell

is often four inches in length, while the animal, with its huge

yellowish foot and dark-colored mantle, which is thrown back,

almost concealing the shell upon its back, is much larger. The

apical perforation is very large. Shell flattened, with radiating,

rounded, crowded ribs; brownish-white in color; edge crenulated;

within pure white. It is found at Monterey, but live specimens are

not very frequently seen near the beach. (Plate LXVI.)

FAMILY ~HALIOTIDÆ~

GENUS ^Haliotis^

This family is closely allied to the /Fissurellidæ/. The species are

known on the Pacific coast by the name of abalone shells, and in

England and the Channel Islands as ormers or sea-ears. There are no

species of /Haliotis/ on the east coast of the United States, but

one has recently been dredged at a considerable depth in West Indian

waters. This family, with the last, possesses the striking anatomical

feature of having the heart traversed by the digestive tract. It

also has two gills, the degree of torsion in the visceral mass not

being sufficient to have crowded out and destroyed the original

right gill. The shell is spiral, but is so greatly flattened, and

the body-whorl is so greatly extended, that the shell quite loses

the spiral appearance. Along the dorsal side of the shell is a row

of holes, through which project numerous tentacular processes from

the mantle. The outer surface of the shell, before it is polished,

is usually rough and unattractive, but within, when the [pg359]

animal is removed, it displays a most beautiful and highly colored

nacreous surface. The spot near the center of the inner shell

surface where the muscles of the foot were attached is usually

most brilliantly colored. The shell of the abalone is susceptible

of taking a very high degree of polish, and is extensively used in

commerce for colored mother-of-pearl and for inlaid work. /Haliotis/

is a vegetable-feeding genus. They cling with great tenacity to rocks

about low tide, and it requires skill to remove them without breaking

the shell. There are several species in California. The Chinese use

the abalone for food, and have waged a persistent war upon the family

along the Pacific coast until the specimens are not nearly as common

as formerly. They are also eaten in France and in Japan.

^H. splendens.^ The largest and perhaps the most attractive in

appearance of the Californian species. Speaking of this beautiful

shell, Professor Keep says: "Within, a whole rainbow is condensed

in one of the magnificent shells, though the shades of green are

most conspicuous. The coloring in the center is particularly fine,

resembling a peacock's tail. There are about six open holes near

one side of the shell, and its length is about the same number of

inches." (Plate LXVI.)

^H. rufescens.^ A large abalone, which sometimes attains a length

of eight or nine inches. It is red in color, with three open holes

in the body-whorl. The outer portion of the shell is usually

incrusted with mineral deposit and overgrown with vegetation.

^H. cracherodii.^ Very dark green without, with five to nine holes;

length from one to six inches; spire exceedingly short. Common on

the Californian coast in crevices of rocks at low tide.

FAMILY ~TROCHIDÆ~

This is one of the largest and most interesting families of the

/Mollusca/. It contains many apparently widely separated genera

and a host of species, which for the most part are littoral, the

majority actually living between tide-marks. The typical trochid

shell is top-shaped or pyramidal, having a broad base and many

closely wound flat whorls terminating in a sharp apex. All the

trochids are nacreous within the aperture--a character which is

constant throughout the family. The animal has but one gill (the

left), a short snout, and often frontal lobes on the head. The

edge of the mantle or the epipodial line of the foot is usually

ornamented with from three to five cirri. The tentacles are [pg360]

long and slender, with short peduncles for the eyes; the operculum

is corneous, with a central nucleus. The animals are herbivorous,

feeding upon algæ. The trochids are essentially tropical shells, and

the most of the genera which are comprised in the family are only to

be encountered in the warm waters of the Pacific and Indian oceans.

Some forms are very beautiful, and frequently are used as mantel

ornaments, and the shells of one little species, which is opalescent

in its coloring, are still extensively gathered in the East Indies,

to be polished and strung like pearls in necklaces.

GENUS ^Margarita^

On the Atlantic coast north of Cape Cod the trochids are represented

by the genus /Margarita/, with five or six species. The shells are

small, thin, and globosely depressed, with smooth or transversely

striated whorls. The aperture is nearly circular, with a simple lip.

[Illustration: /Margarita cinerea./]

^M. cinerea.^ This species has several prominent revolving ridges

upon the upper side of the whorls, with finer ones on the base.

Very fine growth-lines cover the entire shell. It ranges all along

the coast north of Cape Cod, but is not usually found between

tides. The writer has dredged many specimens in shallow water at

Eastport and Bar Harbor.

[Illustration: /Margarita helicina./]

^M. helicina.^ A thinner and more globose species than the last,

with a translucent, shining, smooth surface of a yellowish or olive

color. /M. helicina/ is very fond of the leaves of /Laminaria/, and

is often found clinging to them when storms have torn these great

algæ from the bottom and cast them upon the shore. At Bar Harbor

they are common upon the eel-grass in Rodicks Weir. This species

can generally be distinguished by its iridescent, metallic luster.

[Illustration: /Margarita undulata./]

^M. undulata.^ A commoner species, perhaps, than either of the

preceding, sometimes found on the rocks of sheltered coves at

exceptionally low tides. Judging from the number often to be found

in the stomachs of fishes, they must be considered excellent food

by the cod and its allied species which thrive along the Maine

coast. No doubt millions of /M. undulata/ are yearly destroyed

in this way. The shell is depressed, with four rounded whorls, a

flattish base, and a large umbilical opening. In color it varies

from rose-red to brown. The surface is decorated with numerous

revolving raised lines placed at uniform distances. Just below

the suture the body-whorl is somewhat undulated with short folds.

Height three tenths of an inch, base four tenths of an inch.

[pg361]

GENUS ^Calliostoma^

This genus is better represented on the Pacific coast of the United

States than upon the Atlantic. It comprises a series of marvelously

beautiful shells, often exquisitely colored. They are regularly

conical or pyramidal in shape, with flattened bases. One never tires

in the search for calliostomas. They are not common enough to cause

one to lose interest, and whenever a good specimen is captured it

seems as though one had found some gem cut and polished by nature's

skilful hand and prepared for a place of honor in the cabinet.

^C. occidentale.^ The only species of this genus found on the

northeast coast. It is larger than /Margarita cinerea/, but

somewhat resembles it. It is shining nacreous within and without,

and has strong revolving ribs, the upper one on each whorl often

being broken into a circular row of white dots. The lip is

crenulated. This very pretty species is not likely to be met with

upon the shore, but may be dredged in shallow water on gravelly

bottoms along the Maine coast. Height about one half of an inch.

[Illustration: /Calliostoma occidentale./]

^C. jujubinum.^ A species which occurs in the waters of Florida.

Its form is almost that of a true pyramid. The sutures can scarcely

be distinguished. The shell is marked by brown and purplish-red

spots on a white background, and has numerous revolving ribs broken

into rows of white dots like little glazed beads. The umbilicus

is funnel-shaped and wide. In Tampa Bay this shell is frequently

found on sponges, and may sometimes be gathered on the beach after

storms, even as far north as Hatteras. There are as many as twenty

species of this genus in American Atlantic waters, but they are

either rare or have deep-water stations.

^C. annulatum.^ A remarkable species of /Calliostoma/, found in

California. The whorls are adorned with revolving rows of raised

dots, and the sutures are frescoed in exquisite purple. This

beautiful species lives upon seaweed, and on pleasant days comes

to the surface of the water. It can then be collected from a boat

by drawing in quantities of seaweed. It is very unlikely that the

collector will ever find a specimen upon the beach, for the shell

is too fragile to withstand the rough handling of the waves. Length

one inch.

^C. canaliculatum.^ The largest member of this genus to be found

in American waters. It resembles the last species in form, but

lacks the purple sutures. The revolving ribs are very numerous and

prominent. There is no umbilicus. Length one to one and a half

inches. Found on the Pacific coast.

^C. costatum.^ A heavier shell than the preceding, with somewhat

more rounded whorls. Reddish-brown in color; numerous revolving

ridges; no umbilicus; about three quarters of an inch in length. It

is found in rocky places, and sometimes in considerable numbers,

just at low-tide mark. Found in California. [pg362]

GENUS ^Chlorostoma^

This genus is represented in California by several species, the

commonest of which is probably /C. funebrale/--a doleful name, no

doubt given on account of the jet-black color.

^C. funebrale.^ The shell is thick and strong, like most

between-tide species, which are constantly exposed to the buffeting

of the waves. It is to be found in countless thousands upon rocks

exposed at low tide, and may be gathered at any time except full

flood-tide, like the littorinas and purpuras of the east coast.

Within the aperture the surface is nacreous and greenish in tint;

the last whorl is drawn in, like gathers, at the suture. The

umbilicus is closed. There is a white nodule at the base of the lip

of the columella. Length one half of an inch to one inch. (Plate

LXVII.)

^C. brunneum.^ This species is brown, as its name would indicate,

and there is greenish nacre within the aperture. It lives upon

kelp, or upon rocks at very low tide. Length about an inch. (Plate

LXVI.)

GENUS ^Trochiscus^

^T. norrisi.^ A flattened shell with rounded, dome-like spire and

obtuse apex; a fairly common species. It has a wide, deep umbilicus

and a sharp lip. It is of a rich brown color, with dark chestnut

about the umbilical region and greenish-white within the umbilicus;

there is a band of dark olive-green about the inner margin of the

lip. The shell is about two inches in diameter and of a somewhat

greater height. The operculum is multispiral, with a central

nucleus, and is shaggy and rough. Like all other trochids, it feeds

upon algæ. It is often found upon the beach after violent storms.

Found in California, south of San Francisco. (Plate LXVI.)

GENUS ^Livona^

^L. pica.^ This large and interesting trochid is a West Indian

species which sometimes occurs in Florida. It lives about coral

reefs and rocky shores, attaching itself in vast numbers to the

rocks. This shell is a favorite refuge for large hermit-crabs. It

is a curious sight in certain of the West India islands to see a

/Livona pica/ shell scrambling up a tree, looking very much out of

place upon the back of some terrestrially inclined crustacean. When

well cleaned it is a beautiful shell, with black wavy lines over a

greenish-white nacreous foundation. The animal has a row of waving

cirri upon each side of the mantle, and long, slender tentacles.

It is largely used as an article of diet in the West Indies and

Central America. (Plate LXVII.)

FAMILY ~TURBINIDÆ~

This family is very closely allied to the trochids, the most striking

difference being in the operculum, which in the /Turbinidæ/ is

calcareous and usually smooth and very convex on the outside.

[pg363] The shells are nacreous within, and the animal, with its rows

of waving cirri upon each side, is very suggestive of /Trochus/. They

are, for the most part, shallow-water or littoral forms.

[Illustration: PLATE LXVI. 1, Lucapina crenulata. 3, Chlorostoma

brunneum. 2, Haliotis splendens. 4, Neritina reclivata, enlarged. 5,

Trochiscus norrisi.]

[Illustration: PLATE LXVII. Livona pica, reduced. Turbo castaneus,

enlarged. Nerita peleronta. Chlorostoma funebrale. Nerita tessellata.]

GENUS ^Turbo^

^T. castaneus.^ This species has a range as far north as Cape

Hatteras, and is especially abundant at Tampa, on the west coast of

Florida. The peculiar operculum is sufficient to identify the genus

at once. One variety of this species has a crenulated shoulder upon

the body-whorl and is referred to as ^Turbo crenulatus^, A series

of intermediate forms establishes the specific identity of the two

varieties. (Plate LXVII.)

FAMILY ~NERITIDÆ~

The /Neritidæ/ are strictly littoral forms, almost entirely confined

to the warmer waters of tropical seas. The animal preserves the usual

diatocardian features--has a short snout and long tentacles. Unlike

the trochids and /Turbo/, it has no cirri along the epipodial margin.

The shells are peculiarly shaped, the spire being greatly flattened

and scarcely noticeable on account of the unduly large development

of the body-whorl; thus the shell takes on a decidedly patelliform

appearance. It is without an umbilicus. In the principal genus

/Nerita/ the outer lip is sharp on the edge, but greatly thickened

just within.

GENUS ^Nerita^

^N. peleronta.^ This shell has two teeth on the wide, flat

columellar lip, and about them is a blotch of red, suggesting

blood. The common name of this shell, "bleeding-tooth," is very

appropriate. Found in southern Florida. (Plate LXVII.)

^N. tessellata^ is a smaller species, with heavy revolving ribs,

and is further decorated with transverse oblique black lines. The

operculum is calcareous. Both of these species have the habit of

absorbing the entire inner portion of their shells. They belong

to the West Indian fauna, and occur in great numbers on rocky or

coral shore stations. They also may be found on the east Florida

coast, well to the south. A third species, ^N. versicolor^, often

occurs, associated with the other two. It is somewhat smaller than

the others and can easily be distinguished by the four teeth on

the columellar lip, the edge of the columella being convex. (Plate

LXVII.)

GENUS ^Neritina^

The genus /Neritina/ is very closely allied to the last, having quite

the same form of shell; but it is usually more globular and [pg364]

variously ornamented by bright spots or zigzag lines of coloration.

The neritinas have acquired the habit of ascending rivers, until

they have become almost wholly a brackish- or fresh-water genus.

The metropolis of this genus is in the South Sea Islands, where it

attains a wonderful development in the clear running streams of the

volcanic islands.

^N. reclivata.^ A very pretty olive-green species, with very

fine, wavy, longitudinal lines of coloration, found in almost

all Floridian streams above the action of the tide. The nacre of

the columella and within the aperture is bluish-green, and the

operculum is rich olive. (Plate LXVI.)

^N. viridis.^ A small, intensely green species, which, unlike most

neritinas, is strictly marine. It belongs to the great West Indian

faunal province, but is occasionally found upon the shores of

Florida and of Texas.

The prosobranch gasteropods thus far considered (belonging to the

suborder /Diatocardia/) all show by their anatomical structure that

the process of visceral torsion, though carried very far within them,

has not been complete enough to crowd out and finally destroy one

of each of the paired organs. Both auricles of the heart (with some

exceptions) were left intact.

SUBORDER ~MONOTOCARDIA~

In this the second suborder of the prosobranch gasteropods, the

twisting visceral process has been carried to the extreme. The

heart has but one auricle. There is but one gill (on the left

side), and this is attached to the inner side of the mantle flap.

In other respects the presence of certain specialized organs would

probably indicate that gasteropods belonging to this suborder are

a step higher in the scale of life than those which belong to the

/Diatocardia/.

FAMILY ~JANTHINIDÆ~

GENUS ^Janthina^

The genus /Janthina/ has an exceedingly thin and semi-transparent

shell, deep violet in color on the base and lighter blue on the

spire. An interesting feature of this genus is the mode of depositing

the ova. The female exudes from a gland in the foot a [pg365]

glutinous secretion which hardens in water, and, being filled with

air-bubbles, constitutes a float. On the under side of this are

deposited the eggs in rows of little capsules. While attached to this

float it is impossible for a /Janthina/ to sink, and hence it is that

so many of these creatures are sacrificed in onshore gales of wind.

^J. fragilis.^ The shell of this species is so brittle and fragile

that it is very clearly not adapted to a life near shore. It is in

reality a pelagic species which is occasionally blown ashore during

easterly gales along the Atlantic coast of the United States. Vast

numbers of these pretty creatures are sometimes encountered far out

at sea, floating quietly on the surface. When storms drive them

upon the beach, they become utterly helpless; since their foot

is not adapted for crawling upon the sand, they soon perish, and

their brittle shells are demolished by the surf. In Florida the

beaches are sometimes fairly lined with /Janthina/ shells, which

make a band of purple along the high-tide mark as far as the eye

can reach; then it may be years before they again appear. (Plate

LXVIII.)

[Illustration: /Janthina fragilis/: /FL/, float; /O/, ova; /Pr/,

proboscis; /Br/, branchiæ; /F/, foot.]

FAMILY ~SCALIDÆ~

GENUS ^Scala^

The shells of /Scala/ have such a peculiar scheme of decoration

that once seen they can never be mistaken. They are generally

pure white, with well-rounded whorls, all of which are crossed

at even distances by greatly elevated and smooth ribs. Each rib

represents a rest-period, when the creature thickened the rim

of the shell-aperture. The aperture is generally round, with a

continuous lip. The animal has a retractile proboscis and long,

slender tentacles with eyes at the outer bases, and is a predaceous,

[pg366] carnivorous creature. Some Asiatic species of this genus,

remarkable for their beauty and rarity, have been greatly prized by

collectors. A single specimen of the now well-known ^S. pretiosa^ of

China has been sold for two hundred dollars--a fancy price, indeed,

for a shell which can now be bought for a dollar! There are over

fifty species of /Scala/ on the Atlantic coast, but most of them are

either rare or belong to a zone of deeper water; there are, however,

four or five species which are exceedingly common.

^S. lineata.^ A species which ranges from Hatteras to New England.

It has about eight whorls, and is slightly brownish in color. The

ribs are robust and not greatly elevated; there are from seventeen

to nineteen on the body-whorl. The shell is sometimes painted with

a few revolving brownish lines.

[Illustration: /Scala lineata./]

^S. multistriata.^ The transverse ribs are much smaller but very

numerous; the small spaces between them are marked with many fine

revolving lines. Found from Cape Cod southward.

[Illustration: /Scala multistriata./]

^S. groenlandica.^ Essentially an arctic species, which has found

its way down to the New England coast. It is readily distinguished

by the flattened, coarsely rounded, revolving ribs, which follow

the volutions of the spire. Over them are the usual transverse

heavy ribs peculiar to this genus.

[Illustration: /Scala groenlandica./]

^S. angulata.^ The whorls touch one another only by the ribs,

of which there are nine to each volution. This species has a

remarkably wide range, occurring from Cape Cod to southern Florida.

(Plate LXVIII.)

These four species vary from one half of an inch to one inch in

length. All of them are found on the beach after storms or may be

dredged in shallow water near the shore.

FAMILY ~NATICIDÆ~

This large and interesting family is well represented in the Atlantic

waters of the United States, but its more beautiful members live

in the tropics. The New England and New Jersey species are dull in

color, but offer much of interest to the collector and student. The

foot is enormously large, and carries in front a great shield-like

fleshy process, which curves back over the head of the animal and

serves as a plow in pushing its way through the heavy wet sand of

the beach. When the creature is thus seen extended in the act of

crawling, one wonders how it is possible for it to withdraw so great

an amount of body into its shell; but if it is suddenly seized or

irritated, it will quickly [pg367] demonstrate its ability

to hide itself completely within its house and to close the door

very effectively by means of its operculum. The eyes seem to be

wanting, or they are concealed under the skin of the head. The shell

is usually quite large, with a depressed spire and well-rounded

whorls--especially the body-whorl, which appears to be greatly

swollen. The umbilicus is usually open and moderately large, the lip

simple.

[Illustration: PLATE LXVIII. Janthina fragilis. Sigaretus

perspectivus, upper side. Scala angulata, enlarged. Sigaretus

perspectivus, under side. Natica canrena. Crepidula aculeata.]

GENUS ^Polynices^ (^Lunatia^, ^Natica^).

^P. heros^ (generally referred to as ^Lunatia^ or ^Natica

heros^). One of the commonest large shells and one of the most

characteristic species of the New England and New Jersey littoral

fauna. It is exceedingly common along the Long Island shore, where

it may be found on the open beach, in pools with a sandy bottom

left by the receding tide. It is usually partially and frequently

wholly buried in the sand. The umbilicus is open and large, the

operculum corneous, and the shell heavy and ashy-white to brownish,

with (when young) a yellowish epidermis. Its length is from two to

four inches. It has no ornamentation whatever. /P. heros/ is a most

voracious creature and spends its time in hunting for flesh--either

alive or dead--to devour. It feeds upon dead fish, or upon other

mollusks whose shell it is able to pierce by means of its radula,

making a little round hole through which it sucks out the flesh

from within. The curious egg-cases of this species have already

been referred to. (See Plate I.) It glues together particles of

sand into the form of a basin with the bottom knocked out and

broken on one side. In the gelatinous substance of this basin it

deposits its eggs in a regular order. These hatch out in midsummer.

Egg-cases of this kind can always be found wherever /Polynices/

lives. For a long time naturalists were greatly puzzled by these

curious things, and their blunders are recorded in earlier works,

where these egg-cases have been elaborately described as living

animals belonging to various invertebrate orders. The largest and

best specimens of /P. heros/ are to be found south of Cape Cod.

(Page 343.)

^P. triseriata.^ A small shell of exactly the same shape as /P.

heros/, but decorated with three revolving series of bluish or

chestnut spots. It is pretty well determined that this so-called

species is only the young of /P. heros/. It is very abundant all

along the coast.

[Illustration: /Polynices triseriata/, young; /Polynices

triseriata/, older specimen.]

^P. duplicata.^ This is even more abundant than /P. heros/. It

has a flatter shell, with an obtuse apex and dome-like spire.

The umbilicus is partly or wholly closed by a thick, callous,

shelly process thrown off from the columellar lip, and is chestnut

in color. The surface of the shell is smooth, often polished,

ashy-white below and light chestnut above. The operculum is

corneous. The length of the shell varies in different localities

from one half of an inch to about two [pg368] inches; the breadth

slightly exceeds the length. /P. duplicata/ has a very extensive

range, from the Gulf of Mexico to Newfoundland. The largest and

finest specimens are found in the vicinity of New York and at

Hatteras. In Florida they are usually smaller. This species cannot

be confounded with any other upon our coast on account of the heavy

callous deposit over the umbilicus. Its habits are similar to those

of /P. heros/.

[Illustration: /Polynices duplicata./]

[Illustration: /Natica clausa./]

^Natica clausa.^ A Northern species which is fairly abundant on the

Maine coast. It has a shelly operculum, and the umbilicus is neatly

closed by a pure white, shining callosity. Its length is about one

half an inch, its color livid white to light brown, white within.

The calcareous operculum at once determines this shell. This

species (as well as the following one) has retained the generic

name of /Natica/ because of the shelly operculum, as explained

below.

^N. canrena.^ One of the handsomer species of /Natica/, which

occurs in Florida. Sometimes it is seen as far north as Hatteras.

The shell is white, with bars of light chestnut circling the

whorls, and with zigzag lines of darker purplish hue crossing them.

The base of the shell is white. The aperture is large and flaring,

and is purplish within. The umbilicus is partially closed by an

entering callous plug. The operculum is calcareous, with eccentric,

deeply cut grooves. Found in sandy stations just about low-water

mark. (Plate LXVIII.)

^P. lewisii.^ A species which occurs on the west coast of the

United States. It resembles its New England relative /P. heros/

very closely. /P. lewisii/ is a Northern species, and does not

range south of Oregon. Professor Keep mentions one specimen of the

size of a six-inch globe, but such dimensions are very unusual. A

good-sized specimen need not exceed four inches in height.

^P. recluziana.^ A species well known on the southern coast of

California. The umbilicus is closed by a thick, highly polished

white callosity, and the general shape of the shell is strongly

suggestive of the common east-coast species /P. duplicata/. A large

specimen is about two inches in diameter.

[There has been much confusion in the generic nomenclature of

this family. The old name /Natica/ once did service for all the

species; then the names /Lunatia/, /Neverita/, and /Polynices/ were

applied to certain special forms; but it has been wisely proposed

by conchologists to use the name /Natica/ for those forms having

a shelly operculum, and to adopt the name /Polynices/ for those

having a corneous operculum. /Lunatia/ and /Neverita/ have become

subgenera of /Polynices/.] [pg369]

GENUS ^Sigaretus^

A very interesting species of this genus occurs on the east coast,

sparingly in New Jersey, but very abundantly south of Hatteras.

/Sigaretus/ is a modified /Natica/. The spire is flattened and

minute. The body-whorl, being greatly expanded, gives a wide,

flaring, oblique aperture. The shell is ear-shaped and white, with

fine revolving lines. There is no umbilicus. The operculum is small

and rudimentary. The animal is large, with an enormous foot and

greatly developed propodium, and is a sand-dweller. The common

east-coast form is ^S. perspectivus^. (Plate LXVIII.)

FAMILY ~CAPULIDÆ~

GENUS ^Crepidula^

[Illustration: /Crepidula fornicata./]

^C. fornicata.^ All collectors of mollusks on the Atlantic coast

sooner or later encounter this exceedingly common species adhering

to oyster-shells or scallops, and often to other large live shells.

It is cast upon the beach along the entire length of the Atlantic

coast. The shell is obliquely oval, dull whitish in color, and

either smooth or rough or even ribbed, according to the nature

of the surface to which it clings. The spire is almost entirely

suppressed, the little inconspicuous apex being turned to one

side and closely pressed down against the body of the shell. When

looking into the interior of the shell one is reminded of a boat,

for the upper portion of the aperture is covered by a horizontal

shelly partition, called the diaphragm, a space being left below

which would correspond to the forecastle of a ship. The "stern" is

round, and the "bow" is suggestively pointed.

[Illustration: /Crepidula plana./]

^C. plana.^ In this species the shell is white and flat, or

slightly concave. Although it is pointed at the "bow" end and

square at the "stern," the nautical resemblance stops there,

because, being flat, there are no swelling sides and bow. The

diaphragm is about one half the length of the shell, convex,

shining, white, and translucent. /C. plana/ lives generally within

the aperture of large dead shells. It has a wide range, from Maine

to Florida.

^C. aculeata.^ A common Floridian species which has a remarkable

range, being found in nearly all the tropical and semi-tropical

waters of the world. It is smaller than /C. fornicata/, is

reddish-brown with a white diaphragm, and has several radiating

ribs on the back, which are inclined to be nodulous. (Plate

LXVIII.) [pg370]

On the Pacific coast the following species are found: ^C. adunca^,

with a strongly recurved apex, and less than one inch long; ^C.

rugosa^, rough, brown, with the apex lying on the edge of the

shell, and one inch in length; ^C. navicelloides^, almost identical

with the east-coast /C. plana/. /C. aculeata/ also appears.

GENUS ^Crucibulum^

/Crucibulum/ has a peculiar rounded shield-like form, with a very

small apex on one side. Within there is a cup-shaped appendage

attached by one side to the inner margin of the shell. This latter

feature at once determines the genus.

[Illustration: /Crucibulum striatum/, from above.]

[Illustration: /Crucibulum striatum/, from below.]

^C. striatum.^ This species has radiating riblets, cut by circular

lines of growth. No dimension would quite reach an inch. It is a

common shell on the Atlantic coast, and will be found adhering

to stones and other shells, but it is not, strictly speaking, a

littoral species.

^C. spinosum.^ The shell exhibits a strong tendency to spinous

processes on its back. Found along the southern part of the

California shore.

FAMILY ~LITTORINIDÆ~

GENUS ^Littorina^

/Littorina/ is probably the most characteristic genus of Northern

littoral regions. Together with some of its allied genera it is also,

probably, equally characteristic of various tropical littoral faunas

all over the world. The family comprises strictly between-the-tides

genera and species. Indeed, it is suspected that some species of

/Littorina/ are making very fair progress toward a terrestrial

condition, for they actually live above high-tide mark,--even in

the branches of overhanging trees,--and must certainly pass days at

a time out of their natural element. That such a transformation is

possible need not for a moment be doubted, for there are many land

mollusks to-day that give abundant evidence of having been at some

past time aquatic or marine species. These changes in nature are

constantly going on, and the gradual substitution of a lung for a

gill is no very startling metamorphosis. [pg371]

The littorinas fairly swarm in favorable localities upon all shore

stations. In Maine and Massachusetts the bold, rocky coast furnishes

a home for several species. Often the rocks at low tide are black

with them; the algæ that cling in wet masses to the exposed rocks

are alive with them. One cannot walk about in such localities

without crushing hundreds of specimens. Sometimes they will be found

clinging in clusters upon the piling of old wharves, or crawling

about the bottom at or about the low-tide mark. The best specimens

of /Littorina/ are found in stations where they are bathed twice a

day by pure, uncontaminated sea-water; those living near the mouths

of streams, or where the water is brackish or impure, are usually

small and degenerate. They are vegetable feeders, and have received

the common name of "periwinkles." In Great Britain they are used

among the poorer classes for food. The animal has a short, broad

muzzle, and eyes at the outer bases of the tentacles. The foot is

longitudinally grooved, and there is a rudimentary siphonal fold in

the mantle. The shells are turbinated, usually heavy, few-whorled,

and with a round aperture.

[Illustration: /Littorina litorea./]

^L. litorea.^ This is supposed to be an importation from the Old

World--to have come over by way of Iceland and Greenland, and

then to have migrated down the Labrador coast. For many years

Cape Cod formed a barrier to its advance, but now the species is

abundant at Newport, and is reported at New York. It occurs on

the Maine coast in astonishing numbers, living in vast colonies

on the rocks exposed at low tide. The shell is thick, imperforate

(no umbilicus), and usually has flat, spiral ribs. The columella

is broad and white; the lip thin and black. The general color

varies from black to olive or to dingy gray--sometimes reddish.

The operculum is corneous, with the nucleus near the outer edge.

Despite the variableness of this very common shell (the variations

being chiefly in the height of the spire), it has certain

unmistakable characteristics which, once seen, will enable the

collector to determine it at once.

[Illustration: /Littorina rudis./]

^L. rudis.^ A smaller species than the last. It is strong

and coarse, with revolving grooves and ribs, or smooth, with

interrupted whitish bands and spots. A very common variety of

this species is much smaller than the typical form, being about

one sixth to one fourth of an inch long, smooth, with white and

yellowish spots on olive. It clings to the rocks near high-tide

mark, and is usually found attached to its resting-place by a

bit of hardened mucus. While the typical /L. rudis/ is heavy and

banded, with a moderately high spire and no color, this [pg372]

variety is thinner, with a higher spire and smoother surface,

and has a color-scheme of decoration. It would be impossible

to disconnect the two, for a large series of specimens will

demonstrate beyond doubt, through every minute degree of variation,

that the two forms belong to one and the same species. The station

of /L. rudis/ is much the same as that of /L. litorea/, but the

smaller colored variety of /rudis/ prefers quieter and more

sheltered spots. It is occasionally found on reeds and grasses,

on the piling of wharves, on large boulders above the line of

algæ, and on algæ. It has been the writer's experience not to find

/rudis/ and /litorea/ associated together.

[Illustration: /Littorina palliata./]

^L. palliata.^ A low-spired, globular shell with a large, tumid,

smooth body-whorl. The columella is flattened, curved below, and

imperforate. The color is exceedingly variable, but is usually

bright, shining olive, and this is especially the case with those

individuals that find their station in the dense masses of algæ

that form so conspicuous a feature of a low-tide scene on a rocky

New England coast. From pure olive-green to yellow or bright red,

with revolving black bands, seems a long chromatic leap, but it

is not too great for the Designer of these pretty little globular

shells. As a rule, the color of the shell simulates pretty closely

that of the seaweed upon which it lives, and inexperienced eyes

may easily overlook hundreds of specimens, all within close reach.

The banded varieties are less common. The head of the animal is

somewhat orange in color, the foot slate. The distinguishing

features of this species are the smooth, globular shell, the low

spire, the broadly flattened columella, and the orange-colored head

of the animal. It is found on /Fucus/ between tides, and often

associated with /L. rudis/, on the whole coast north of New Jersey.

The three preceding species are distinctly boreal in their range,

but their place is taken in southern Atlantic waters of the United

States by the following exceedingly common species:

[Illustration: /Littorina irrorata./]

^L. irrorata.^ A solid, robust shell, which attains a length of

about one inch. It is in many respects suggestive of /L. litorea/,

its Northern relative, but the spire is higher, with straighter

outlines, and the apex is acute. The surface is ornamented with

closely set, revolving ribs; the sutures are indistinct; the lip

is thin, though thickened just within; and the color is whitish to

pale cinereous greenish, sometimes spotted with broken brownish

lines. Within it is white, with a reddish tinge on the columella,

and brownish spots on the edge of the lip. This species ranges from

Maryland to Texas; its station is between tides.

^L. angulifera.^ As the last species resembles /L. litorea/, so

this other common Southern form resembles a greatly developed and

large /L. rudis/ of the smoother variety. It has a high-spired

shell, with an acute black tip. It has about six whorls, which are

variously decorated by wavy, oblique black lines and revolving

black lines broken into series of dots and larger spots near the

suture. The ground-color varies from yellow to purple. None of

the colors are very vivid. Within it is yellowish-white. This

species has a much thinner and more delicate shell than any of

the littorinas thus far considered. It is common on the piling of

wharves and in sheltered nooks everywhere [pg373] between tides.

It is essentially a tropical species of very wide and extended

range, but it does not occur north of St. Augustine. At Tampa it

has been found in vast numbers. (Plate LXIX.)

The California coast furnishes two more species of /Littorina/.

Their station is among the rocks between tides, and their habits

are quite the same as those of the east-coast species.

^L. scutulata.^ In this species the color is of various shades,

generally dark gray, mottled with white spots. A good-sized

specimen measures one half of an inch in length. The spire is high;

the columella flattened, broad; the shell is purplish-white within

the aperture. (Plate LXIX.)