upon one another, a movement which is prevented in the Testicardines
by the hinge. In very young transparent specimens François was able
to observe the movements of the fluid in the system of tubules which
penetrate the mantle; these tubules are figured by him, and Fig. 315 is
taken from his illustration.
Davidson in his Monograph on the British Fossil Brachiopoda states
that the largest “recent Brachiopod which has come under my notice is
a specimen of _Waldheimia venosa_ Solander, measuring 3 inches 2 lines
in length, by 2 inches in breadth, and 1 inch 11 lines in depth.” It
was found in the outer harbour of Fort William, Falkland Islands, in
1843. A specimen of _Terebratula grandis_ from the Tertiary deposits,
however, exceeds this in all its dimensions. Its length was 4½ inches,
its breadth 3 inches 2 lines, and its depth 2 inches 2 lines.
=Distribution in Space=
Brachiopods are very localised; they live in but few places, but when
they are found they usually occur in great numbers. During the cruise
of the _Challenger_, dredging was conducted at 361 stations; at only
38 or 39 of these were Brachiopoda brought up. Mr. Cuming, quoted
by Davidson, records that after a great storm in the year 1836, he
collected as many as 20 bushels of _Lingula anatifera_ on the sea-shore
at Manilla, where, he relates, they are used as an article of food. It
has been suggested above that their abundance in certain localities is
due to their limited powers of locomotion, which are effective but for
a few hours, the larva being, moreover, so minute that unless borne by
a current it could not travel far from its parent. When once settled
down it has little to fear from the attacks of other animals. The
size of its shell relative to its body would deter most animals from
regarding it as a desirable article of food, and as far as is known
at present the Brachiopoda suffer but little from internal parasites,
the only case I know being a minute parasitic Copepod belonging to a
new and as yet unnamed genus which I found within the mantle cavity
of _Cistella_ (_Argiope_) _neapolitana_ in Naples. Their slight value
as an article of diet has doubtless helped to preserve them through
the long periods of geological time, through which they have existed
apparently unchanged.
Two of the recent genera of the family Lingulidae, _Lingula_ and
_Glottidia_, are usually found between tide-marks or in shallow water
not exceeding 17 fathoms. _Discina_ is also found about the low-tide
level, but one species at any rate, _Discinisca atlantica_, has been
dredged, according to Davidson, “at depths ranging from 690 to nearly
2425 fathoms.” Their larvae frequently settle on the shells of their
parents, and thus numbers of overlapping shells are found clustered
together. _Crania_ is usually dredged from moderate depths down to 808
fathoms, adhering to rocks, lumps of coral, stones, and shells.
Of the Testicardines, _Terebratula Wyvillei_ has probably been found at
the greatest depth, _i.e._ 2900 fathoms, in the North Pacific. It is
interesting to note that its shell is glassy and extremely thin. The
Brachiopoda are, however, as a rule, found in shallower water; they
abound up to a depth of 500 or 600 fathoms, after which they rapidly
diminish with increasing depth. About one-half the named species occur
at a depth of less than 100 fathoms.
The vertical range of depth of certain species is great; _Terebratula
vitrea_ is recorded from 5 to 1456 fathoms, _T. Wyvillei_ from 1035
to 2900 fathoms. This is to some extent explicable since, after a
certain depth has been reached, many of the external conditions, such
as absence of temperature and light, must remain constant even to the
greatest depths of the ocean.
The area of the ocean explored by dredging forms such an infinitesimal
fraction of the whole, that it seems superfluous to consider the
horizontal distribution of Brachiopods. A few facts may, however,
be mentioned. Certain species, as _Terebratula vitrea_, _T. caput
serpentis_, _Waldheimia cranium_, _Megerlia truncata_, and _Discinisca
atlantica_, have a very wide if not cosmopolitan distribution. The
second of the above named extends as far north as Spitzbergen, and as
far south as Kerguelen Island. Many species are, on the other hand,
very localised, and have hitherto only been found in one place. A very
considerable number of these have been dredged off Japan and Korea, and
this region may be to some extent regarded as the headquarters of the
group.
The following species have been obtained within the limits of the
British Area, as defined by Canon Norman, who has been good enough to
revise the list, which is founded on that drawn up by Davidson in his
Challenger Report. Their range of bathymetric distribution is given in
the column on the left.
Depth in
Fathoms
0 to 1180. _Terebratulina caput Oban, and off Cumbrae
serpentis_ Lin. Islands, Loch Torridon,
Scotland, off Belfast
8 to 25. _Terebratula (Gwynia) Belfast Bay, E. and S.
capsula_ Jeff. coast of Ireland,
Plymouth, Weymouth, and
Guernsey
5 to 690. _Waldheimia cranium_ Müller North British seas. Off
Shetland
75 to 725. _Waldheimia septigera_ Lovén North British seas. Off
Shetland
20 to 600. _Terebratella N.N.W. of Unst, Shetland
spitzbergenensis_ Dav.
18 to 364. _Argiope decollata_ Chemnitz Two miles east of
Guernsey
20 to 45. _Cistella cistellula_ S. Wood Shetland, near Weymouth,
S. coast of England
650 to 1750. _Atretia gnomon_ Jeff. W. of Donegal Bay in 1443
faths. Between Ireland
and Rockall, in 1350
faths.
10 to 690. _Rhynchonella psittacea_ Shetland and near Dogger
Gmelin. Bank. This species is
possibly fossil as well
as recent
3 to 808. _Crania anomala_ Müller Loch Fyne, North of
Scotland
690 to 2425. _Discinisca atlantica_ King W. of Donegal Bay in 1366
faths., W. of Ireland in
1240 faths., off Dingwall
Bay
=Classification=
The table of classification here appended is that suggested by Mr.
Davidson in his Monograph on the Recent Brachiopoda.
I. TESTICARDINES
Family
A. TEREBRATULIDAE. This includes the majority of genera and of
species, the latter, without counting
uncertain species, amounting to sixty-eight.
Examples: _Terebratula_, _Terebratella_,
_Terebratulina_, _Waldheimia_,_Megerlia_,
_Argiope_, _Cistella_.
B. THECIDIIDAE. This family contains one genus, _Thecidium_,
with two species.
C. RHYNCHONELLIDAE. This family is made up of eight species,
six of which belong to the genus
_Rhynchonella_, and two to _Atretia_.
II. ECARDINES
D. CRANIIDAE. This family comprises the four species of
_Crania_.
E. DISCINIDAE. This family contains one species of
_Discina_ and six of _Discinisca_.
F. LINGULIDAE. This family consists of eight species of
_Lingula_ and three of _Glottidia_.
It is impossible to come to any satisfactory conclusion as to the
position of the group Brachiopoda with relation to the rest of the
animal kingdom. They have, in accordance with the views of various
investigators, been placed in close connexion with many of the large
groups into which the Invertebrates are split up. The Mollusca, the
Tunicata, the Polyzoa, the Chaetopoda, the Gephyrea, and of recent
times such isolated forms as _Phoronis_ and _Sagitta_, have all in turn
had their claims advanced of relationship to this most ancient group.
As far as I am in a position to judge, their affinities seem to be
perhaps more closely with the Gephyrea and with _Phoronis_ than with
any of the other claimants; but I think even these are too remote to
justify any system of classification which would bring them together
under a common name. Investigation into the details of the embryology
of the group, more especially into that of the Ecardines, might throw
some light on this subject, and it is much to be desired that this
should be undertaken without delay. That the group is a most ancient
one, extending from the oldest geological formations, we know, that the
existing members of it have changed but little during the vast lapse
of time since their earliest fossil ancestors flourished, we believe;
but we are in almost total ignorance of the origin or affinities of
the group, and we can hardly hope for any light on the subject except
through embryological research.
BRACHIOPODA
PART II
PALAEONTOLOGY OF THE BRACHIOPODA
BY
F. R. COWPER REED, B.A., F.G.S.
Trinity College, Cambridge
CHAPTER XVIII
PALAEONTOLOGY OF THE BRACHIOPODA
INTRODUCTION--DIVISION I. ECARDINES--EXTERNAL
CHARACTERS--INTERNAL CHARACTERS--DIVISION II.
TESTICARDINES--EXTERNAL CHARACTERS--INTERNAL
CHARACTERS--SYNOPSIS OF FAMILIES--STRATIGRAPHICAL
DISTRIBUTION--PHYLOGENY AND ONTOGENY
=Introduction=
The wide distribution and vast abundance of the Brachiopoda throughout
the whole series of geological formations make this group of especial
importance to the student of the past history of the earth; and the
zoologist must always regard the fossil forms with peculiar interest,
because they not only largely outnumber the living representatives,
but comprise numerous extinct genera, and even families, exhibiting
types of structure and characters entirely absent in the modern
members of the group. It is a most fortunate circumstance that the
excellent state of preservation in which we frequently find them, and
the immense amount of material at our disposal, enable us to determine
with accuracy and certainty the internal characters of the shells in
the great majority of cases. But it is only since the beginning of the
present century that our knowledge of the anatomy of the soft parts
of the living animal has rendered any tracing of homologies possible.
In the case of features in fossil extinct types the interpretation
must be to some extent doubtful. Barrande, Clarke, Davidson, Hall,
King, Oehlert, Waagen, de Verneuil, and a host of other workers have
contributed to the information which we now possess; and their works
must be consulted for details of the subject.[428]
Since all Brachiopods are inhabitants of the sea, the geologist at once
recognises as a marine deposit any bed which contains their remains.
Under favourable conditions they swarmed in the seas of Palaeozoic
and Mesozoic times. Beds of limestone are frequently almost entirely
composed of their shells, as, for instance, some of the Devonian
limestones of Bohemia. Often they give the facies to the fauna and
outnumber in species and individuals all the other organisms of the
period. The Ungulite Sandstone (Cambrian) of Russia and the Productus
Limestone of the Salt Range in India of Carboniferous and Permian age
are well-known examples.
Many species seem to have been gregarious in habit; thus _Productus
giganteus_ of the Carboniferous Limestone may generally be found in
crowded masses, as in some localities in Yorkshire.
The fact that certain species of Brachiopods characterise definite
stratigraphical horizons or “zones” gives them occasionally an
importance equal to that of Graptolites; for instance, the Ecardinate
species _Trematis corona_ marks a set of beds in the Ordovician, and
the isolated _Stringocephalus Burtini_ is restricted to the upper part
of the Middle Devonian, giving to the limestone on that horizon its
distinctive name. It is noteworthy also how certain species affect a
sandy and others a calcareous sea-bottom, so that beds of the same
age show differences in their Brachiopod fauna owing to a dissimilar
lithological composition.
While few of the recent Brachiopods reach a large size, some of the
extinct species measure several inches in breadth, but the great
_Productus giganteus_ attained the width of even a foot.
The bright colours of the shells of the living animals are not
generally preserved amongst the fossil species from the older rocks;
yet in a Carboniferous _Terebratula_ we can even now detect the purple
bands in some specimens, and a Cretaceous _Rhynchonella_ similarly
exhibits its original colour.
The Brachiopoda are evidently a group in its decline, as the geological
record shows; but they date back from the earliest known fossiliferous
rocks, in which the Ecardinate division is alone represented. As we
ascend through the stratigraphical series the number and variety of
genera and species belonging to both divisions rapidly increase until
in the united Ordovician and Silurian there are nearly 2000 species and
about 70 genera. From this point of maximum development down to the
present day there is a gradual decrease in numbers.
According to Davidson, at least 17 Upper Tertiary species are still
living on our sea-bottoms; and many recent Mediterranean forms occur in
the Pliocene rocks of the islands and shores of that sea, and in the
Crags of East Anglia.
A brief review of the chief characteristics of fossil Brachiopoda
is given below. Those genera which have the greatest zoological or
geological importance can alone be noticed owing to the exigencies of
space.
I. ECARDINES
=External Characters=
A considerable diversity of external form is met with even in this
division, from the limpet-like _Discina_ to the flattened tongue-shaped
_Lingula_. The valves have most commonly a smooth external surface with
delicate growth-lines; but sometimes pittings (_Trematis_) or radiating
ribs (_Crania_) are present, and in a few forms the shell is furnished
with spines (_Siphonotreta_), which perhaps serve to anchor it in the
soft mud of the sea-bottom. The usual mode of fixation was by means of
the pedicle (= peduncle or stalk), which either (1) passed out simply
between the posterior gaping portion of the valves (_Lingula_), or (2)
lay in a slit in the ventral valve (_Lingulella_), or (3) pierced the
substance of the latter valve by a definite foramen (_Discina_). The
first-mentioned condition of the pedicle seems the most primitive.
Rarely the pedicle was absent, and the shell was attached by the whole
surface of the ventral valve (_Crania_, p. 467).
The two valves in the fossil Ecardines were held together by muscular
action, though in some families (_Trimerellidae_) we see traces of
articulating processes. The “hinge line,” or line along which the
valves worked as on a hinge, is in most forms more or less curved. A
“hinge area” (_i.e._ that portion of the shell generally smoother than
other parts of the valves, more or less triangular in form, and lying
between the beaks on one or both sides of the hinge line), is usually
absent in the Ecardines.
[Illustration: FIG. 322.--Muscle-scars of _Lingula anatina_.
Inner surface of =A=, Pedicle-valve or ventral valve. =B=,
Brachial or dorsal valve; _p.s_, parietal scar; _u_, umbonal
muscle; _t_, transmedians; _c_, centrals; _a.m.e_, laterals (_a_,
anteriors; _m_, middles; _e_, externals).]
[Illustration: FIG. 323.--_Trimerella._ (After Davidson and
King.) =A=, Inner surface of pedicle-valve or ventral valve: _a_,
pseudo-deltidium; _b_, deltidial slope; _c_, deltidial ridges;
_d_, areal borders; _e_, cardinal callosities; _f_, cardinal
facet; _g_, lozenge; _i_, umbonal chambers separated by cardinal
buttress; _j_, platform; _k_, platform vaults; _l_, median plate;
_m_, median scars; _n_, anterior scars; _o_, lateral scars; _p_,
post-median scars; _q_, crown crescent; _r_, side or lateral
crescent; _s_, end or terminal crescent; _t_, transverse scars;
_u_, archlet (vascular sinuses); _w_, sub-cardinal scars; _x_,
umbo-lateral scars. =B=, Brachial or dorsal valve: _e_, cardinal
sockets; _j_, platform; _k_, platform vaults; _l_, median plate;
_m_, median scars; _n_, anterior scars; _q_, crown crescent; _r_,
side or lateral crescent; _s_, end or terminal crescent; _t_,
transverse scars; _u_, archlet (vascular sinuses); _v_, cardinal
scars; _w_, sub-cardinal scars.]
=Internal Characters=
Owing to the rarity of well-preserved interiors of valves in this
division, our knowledge of their internal characters is still far
from satisfactory. The arrangement of the muscular impressions varies
greatly amongst extinct genera, but we are often able to interpret
them with a considerable amount of certainty by a study of the scars
and the muscles of the well-known recent _Lingula_ (Fig. 322). The
extreme specialisation of the muscles in many of the earliest genera
(_e.g._ _Lingula_) is remarkable, and points to a long but so far
undiscovered ancestry in pre-Cambrian times.[429] In fossil species
of _Crania_ and _Lingula_ the muscle-scars correspond closely with
those in the living representatives of these genera. In the most
highly specialised family of the Ecardines--the _Trimerellidae_--we
meet with features of peculiar interest.[430] The muscle-scars in this
family (Fig. 323, A, B) are most remarkable for the development of the
so-called “crescent,” (_q.r.s._) which skirts the posterior margin of
both valves as a sub-cardinal impression. It is believed to be the
trace of a strong post-parietal muscular wall, analogous in position
to that of _Lingula_. The three pairs of “lateral” muscle-scars in
the latter genus seem to be represented by the “terminal” (_s_) and
“lateral” (_r_) scars on the crescent of the _Trimerellidae_. A
pair of “transverse” scars (_t_) occurs in each valve between the
“terminals” and the antero-lateral edge of the “platform” (_j_).
“Cardinal” (_v_), “sub-cardinal” (_w_), and “umbo-lateral” (_x_) scars
also occur. The median impression which covers the “platform” (_j_)
consists of a central, lateral, and usually an anterior pair of scars;
and the impressions of the genital organs, according to Davidson
and King, lie medianly posterior to the “platform.” The “platform”
itself is a more or less conspicuous central calcareous elevated area
occurring in each valve, but most developed in the dorsal; in some
cases it is double-chambered with tubular cavities (“platform vaults,”
Fig. 323, A, B, _k_), in others it is more or less solid. It appears to
have originated through a posterior shifting of the central muscular
bands, that they might be inserted behind the liver; at the same time a
deposition of shelly material, to form fulcra to work the heavy valves,
took place at these points. The tunnelling-out of the platform was
probably due to the continual pressure of the lobes of the liver. The
division of the umbonal cavity into definite chambers in _Monomerella_,
and to a less extent in other members of this family, appears,
according to Davidson and King, to have been caused by pressure of the
ovarian lobes.
In connexion with the foregoing remarks on the development of the
“platform,” it may be mentioned that the paths along which the
muscle-bands move, as the shell of Brachiopods increases in size, are
marked by elongated scars, and often by shelly deposits; and when the
members of a muscle-pair come into juxtaposition these shelly deposits
(which act as fulcra for the muscles) combine, and by the growth
of the shell form a septum, as in the case of the median septum of
_Lingulepis_.
The _Obolidae_ show some important features in the internal
impressions. _Obolella crassa_ (Hall) may be taken as a well-known
type of the family. In this species a pair of small scars, one on each
side of the pedicle-groove, lies close under the hinge line in the
ventral valve. There is also a well-marked scar for the insertion of
the pedicle-muscle at the end of the pedicle-groove. A pair of much
elongated lateral impressions extending forward from the “cardinals”
may be homologous with the “laterals” of _Lingula_; and the two small
central scars between them may be compared with the “centrals” of
_Lingula_ which are in a somewhat similar position. In the dorsal valve
of _O. crassa_ a pair of “cardinals” is found, and on each side of a
low median rounded ridge are two small “central” scars. Indistinct
“lateral” scars arise close to or in the central area, and diverge
anteriorly.
Sometimes a great concentration of muscle-scars occurs round the
foramen in the ventral valve, as in _Siphonotreta_.
As regards the minute structure and composition of the shell in
the Ecardines, we find that the _Lingulidae_ and _Discinidae_ have
their shell composed of alternating layers of phosphate of lime and
a corneous substance; the former layers are pierced by microscopic
canals. The _Craniidae_ have calcareous shells traversed by tubules,
which divide into many fine branches near the external surface; a thin
periostracum covers the exterior. The _Trimerellidae_ have heavy thick
calcareous shells, for which they required the previously-described
elaborate arrangement of muscles to open and shut them.
II. TESTICARDINES
=External Characters=
It is to this division that the great majority of the Brachiopoda
belong; and the diversity of form, of ornamentation, and of internal
characters is correspondingly greater than in the Ecardines.
A transversely or longitudinally oval shape of shell is the commonest;
but sometimes it is triangular, as in _Rhynchonella_ (Fig. 327), or
bilobed, as in _Pygope_ (= _Terebratula diphya_). The ventral valve is
usually more convex than the dorsal, and the former may be prolonged
into a tube by the accelerated growth and infolding of the anterior
and lateral margins, producing a very abnormal form (_Proboscidella_).
The external surface of the valves is frequently ornamented with more
or less prominent radiating ribs; and fine concentric growth-lines
are commonly shown, and may be developed into coarse ridges or
wrinkles, particularly in old individuals. The members of the family
_Productidae_ are usually furnished with tubular spines, which are
sometimes of great length, and served to anchor the free shells in the
mud, or were twisted round Crinoid stems and similar objects.
In the ventral valve of many genera there is a median sinus, with
a corresponding fold in the dorsal valve, and rarely _vice versâ_;
sometimes the fold and sinus are double.
The hinge line is either curved or straight, and the valves are
articulated by means of a pair of “hinge-teeth” (Fig. 329, _t_) in the
ventral valve, which fit into corresponding sockets in the opposite
valve. Some genera have the teeth very rudimentary, or have lost them
altogether. The teeth are frequently supported by “dental plates,” and
the sockets by “socket plates” (_e.g._ _Conchidium_, Figs. 324, 325).
A few genera with a long hinge line have the whole of it denticulated
(_Stropheodonta_). In the dorsal valve medianly close under the hinge
line is a shelly protuberance--the “cardinal process”--to which
the diductor muscles are attached. It is sometimes of great length
and forked (_Stringocephalus_, Fig. 326), or tripartite, or even
quadripartite; but in _Rhynchonella_ and some other genera it is
rudimentary.
[Illustration: FIG. 324.--_Conchidium galeatum._ Wenlock
Limestone.]
[Illustration: FIG. 325.--_Conchidium galeatum._ Transverse
section. _d_, Dorsal valve; _d.s_, dorsal septum; _s_, socket
plate; _v_, ventral valve; _v.s_, ventral septum; _d.p_, dental
plate.]
[Illustration: FIG. 326.--_Stringocephalus Burtini._ (Modified
from Woodward.) Devonian. =A=, Interior of dorsal valve. =B=,
Side view of interior of shell; _a_, adductor (= occlusor) scars;
_c_, crura; _c.p_, cardinal process; _d.s_, dorsal septum; _h.p_,
hinge plate; _l_, brachial loop; _s.p_, shelly processes; _t.s_,
dental sockets; _v.s_, ventral septum.]
A “hinge area” (Fig. 334, _c.a_) is often present on one or both
valves, and may be of great size, as in _Clitambonites_, but in
_Productus_ it is wholly absent. In those genera that possess it a
triangular fissure--the “deltidial fissure”--frequently traverses it
on both valves; in the dorsal valve the fissure is merely the space
between the dental sockets, and may be occupied by the cardinal-
process (Fig. 334, C) or covered by a shelly plate--the “chilidium.” In
the ventral valve it gives passage to the pedicle, and may be partly
or entirely closed by a similar plate (Fig. 334, _d_) known as the
“pseudo-deltidium,” especially large in _Clitambonites_, or remain
open (_Orthis_). This pseudo-deltidium is a primitive character, and
arises in an early stage of the development as a shell-growth on the
dorsal side of the animal, becoming attached to the ventral valve
subsequently. The pedicle in many genera passes out through a special
foramen in the beak of the ventral valve; and its proximal portion
is often embraced by a pair of small plates--the deltidial plates or
“deltidium”--which are formed on lateral extensions of the ventral
mantle lobe, according to Beecher. These plates lie on each side of the
pedicle, or grow round and unite in front of it (_Rhynchonella_, Fig.
327), or constitute merely its anterior border (_Terebratula_, Fig.
328). In some cases this foramen becomes closed in old age.
[Illustration: FIG. 327.--_Rhynchonella Boueti._ (Cornbrash.)
_d_, Deltidium; _f_, foramen.]
[Illustration: FIG. 328.--_Terebratula sella._ (Lower Greensand.)
_d_, Deltidium; _f_, foramen.]
The dorsal valve in a few cases has its beak perforated by a
foramen--the “visceral foramen.” This foramen is in no way connected
with the pedicle foramen, but points perhaps to the existence in
the early Testicardinate genera of an anal aperture. In _Athyris
concentrica_ (Devonian) this foramen is connected internally with a
cylindrical tube, which extends longitudinally to about one-third the
length of the valve. In _Centronella_ the aperture in the cardinal
plate is rounded and complete; and in _Strophomena_ and its allies
the opening lies between the cardinal processes. If this feature is
correctly interpreted, it suggests a retrogression of the group since
Palaeozoic times not only in numbers, but in structure; and other
evidence points the same way.
=Internal Characters=
The interior of the shell is sometimes more or less divided up by
septa. A median septum occurs in one or both valves of many genera as
a low ridge or strongly developed partition (_Waldheimia_, Fig. 329,
_ss_; and Stringocephalus, Fig. 326, B, _v.s_). _Conchidium_ (Fig. 325)
has its dental plates of great size, and uniting to form a V-shaped
chamber or “spondylium,” supported by a median double septum; and by
means of these with a pair of septa and the large socket-plates in the
dorsal valve the interior of the shell of this genus is divided up into
several chambers.
The interiors of several other genera are somewhat similarly divided up.
[Illustration: FIG. 329.--_Waldheimia (Magellania) flavescens._
=A=, Interior of ventral valve: _a_, adductor scars; _v.a_,
ventral adjustors; _d_, divaricators; _a.d_, accessory
divaricators; _p_, peduncular muscle; _dm_, deltidium; _f_,
foramen; _t_, teeth. =B=, Interior of dorsal valve: _a.a_,
anterior adductor (occlusor) scars; _a.p_, posterior adductor
(occlusor) scars; _c.p_, cardinal process; _cr_, crura; _d.s_,
dental sockets; _hp_, hinge-plate; _l_, brachial loop; _ss_,
septum. (After Davidson.)]
In the Carboniferous genus _Syringothyris_ two special plates, situated
between the dental plates, are rolled into an incomplete tube, so as
to enclose probably the anal extremity of the alimentary canal; and
in several genera a sub-umbonal “cardinal plate” is present, which is
perforated (_Athyris_) or slit in some cases for the passage of the
anal tube.
For the support of the fleshy “spiral arms” the calcareous structures
forming the “brachial apparatus” are of two main types--(1) the loop
type; (2) the spiral-cone type. In the _Strophomenidae_ no special
calcareous support seems to have been usually present (Fig. 334),
though in some species of _Leptaena_ spirally-grooved elevated areas
supported the fleshy arms; in the _Productidae_ it is probable that the
ridges enclosing the “reniform impressions” (Fig. 333, _i_) served for
a similar purpose.
The _Terebratulidae_ show the “loop type” of brachial apparatus. In
_Waldheimia_ (Fig. 329), which may be taken as an example, we notice
first in the dorsal valve the “crura” (_cr_), from which arise the two
“descending branches” which run forwards and then are bent back to form
the “ascending branches” which are united by the “transverse band.” In
some genera the “ascending branches” may be reduced to mere points,
and the “transverse band” become a median vertical plate; the “crura,”
too, may be fused so as to form a “crural band”; and the “descending
branches” may be connected by a cross band--the “jugal band.” In
_Stringocephalus_ (Fig. 326, _l_, _s.p_) the loop is furnished on its
inner edge with radiating processes; and in _Argiope_ the loop is
simple, not reflected, and fused with marginal septa; while in the
_Thecidiidae_ it is more or less fused with the shell itself, and with
the mass of calcareous spicules secreted by the mantle.
The “spiral-cone type” of brachial apparatus is found in the
_Spiriferidae_, _Atrypidae_, and _Koninckinidae_, and consists of two
spirally-enrolled calcified lamellae, forming two cones with their
apices directed laterally (_Spirifera_, Fig. 330), or towards the
interior of the dorsal valve (_Atrypa_, Fig. 332), or towards each
other (_Glassia_); or forming two flat spirals in the same plane
(_Koninckinidae_). A “jugal band” is generally present, but varies much
in position, and in some genera has complicated posterior processes.
The _Rhynchonellidae_ have no loop or spiral cones, but merely a pair
of short “crura.”
[Illustration: FIG. 330.--_Spirifera striata._ (Carboniferous
Limestone.) Showing brachial spires.]
The principal modifications in the attachments of the muscles in the
_Testicardines_ are illustrated by _Productus giganteus_ (Fig. 333),
_Leptaena rhomboidalis_ (Fig. 334), and _Waldheimia flavescens_ (Fig.
329).
In _Productus_ (Fig. 333) we see in the ventral valve a pair of
dendritic occlusor, often called adductor, impressions and a pair of
large flabellate divaricator impressions. In the dorsal valve the large
“cardinal process” served for the attachment of the divaricator, and a
low median septum separated the dendritic occlusor scars, which are
rarely divisible into anterior and posterior pairs.
[Illustration: FIG. 331.--_Atrypa reticularis._ (Wenlock
Limestone.)]
[Illustration: FIG. 332.--Interior of the same, seen from the
dorsal side, showing brachial spires. (After Hall.)]
In _Leptaena_ (Fig. 334) the occlusor scars (_a_) in the ventral valve
are narrow and median, and are enclosed by a pair of flabelliform
divaricator impressions (_d.v_); in the dorsal valve two pairs of
occlusor scars (_a.a_, _p.a_) are well marked, and accessory posterior
occlusor scars are traceable in some specimens. The vascular sinuses
(_v.s_) and genital areas are conspicuous in many species of this and
other genera.
[Illustration: FIG. 333.--_Productus giganteus._ (After
Woodward.) Carboniferous Limestone. =A=, Interior of dorsal
valve. =B=, Interior of ventral valve. =C=, Transverse section
of valves. =D=, Hinge line of =A=: _a_, occlusor scars; _d_,
divaricator scars; _i_, “reniform impressions”; _ca_, cardinal
process; _h_, hinge line; _p_, brachial prominence; _s_, cavity
for spiral arms; _do_, dorsal valve; _ve_, ventral valve.]
In _Waldheimia_ (Fig. 329) a sub-umbonal “peduncular muscle” scar
(_p_) in the ventral valve has before it a pair of “accessory
divaricator” scars (_a.d_) flanked by a pair of “ventral adjustor”
(_v.a_) and a pair of “divaricator” impressions (_d_), between which
lie the two occlusor scars (_a_). In the dorsal valve anterior and
posterior pairs of occlusor scars (_a.a_, _a.p_) are visible.
The minute structure of the calcareous shell of the Testicardines is
of flattened fibrous prisms inclined at a very acute angle to the
surfaces. In many forms minute tubes more or less closely arranged
pierce through the fibrous shell-substance; but in some genera
(_Productus_) they do not reach the outer surface (see p. 468). Allied
genera, however, differ much in the punctate or impunctate character of
the shell.
[Illustration: FIG. 334.--_Leptaena rhomboidalis._ (Silurian.)
=A=, External view of ventral valve. =B=, Interior of ventral
valve: _a_, occlusor scars; _d_, pseudo-deltidium; _d.v_,
divaricator scars; _c.a_, hinge area; _t_, teeth. =C=, Interior
of dorsal valve: _a.a_, anterior occlusor scars; _p.a_, posterior
occlusor scars; _c.a_, hinge area; _c.p_, cardinal process; _d_,
chilidium; _s_, dental sockets; _v.s_, vascular sinuses.]
SYNOPSIS OF FAMILIES
I. ECARDINES
Family. _Lingulidae_
Shell elongated, composed of alternating chitinous and
calcareous layers, the latter of which are perforated. Attached
by a pedicle passing between apices of valves.
Arms have no calcified supports.
(For muscles see Fig. 322.)
RANGE.--Lower Cambrian to Recent.
PRINCIPAL GENERA.--_Lingula_, _Lingulella_, _Lingulepis_.
Family. _Obolidae_
Shell varies in shape. Ventral valve provided with pedicular
groove or foramen. Cardinal border thickened. No brachial
supports. Shell composed of alternating chitinous and calcareous
layers.
(For muscles see p. 496.)
RANGE.--Lower Cambrian to Devonian.
PRINCIPAL GENERA.--_Obolus_, _Obolella_, _Kutorgina_,
_Linnarssonia_, _Siphonotreta_, _Acrotreta_, _Neobolus_.
Family. _Discinidae_
Shell rounded, valves more or less conical, fixed by pedicle
passing through slit or tubular foramen in ventral valve. No
calcified brachial supports. Shell structure chitino-calcareous.
RANGE.--Ordovician to Recent.
PRINCIPAL GENERA.--_Discina_, _Orbiculoidea_, _Trematis_.
Family. _Craniidae_
Shell calcareous, subcircular; fixed by surface of ventral
valve; dorsal valve the larger, depressed-conical. Shell
structure punctate.
Four principal muscular scars in each valve, with central
triangular protuberance in ventral valve (see p. 476).
RANGE.--Ordovician to Recent.
PRINCIPAL GENUS.--_Crania_.
Family. _Trimerellidae_
Shell thick, calcareous, inequivalve; beak of ventral valve
usually prominent; rudimentary teeth maybe present; hinge area
well developed, with pseudo-deltidium. In interior of valves
muscular platform, “crescent,” and sometimes sub-umbonal
chambers (see p. 494, Fig. 323).
RANGE.--Ordovician and Silurian; maximum in Wenlock.
PRINCIPAL GENERA.--_Trimerella_, _Monomerella_, _Dinobolus_,
_Rhinobolus_.
II. TESTICARDINES
Family. _Productidae_
Shell entirely free, or fixed by ventral valve or spines.
Concavo-convex, more or less covered with tubular spines. Hinge
line straight. Hinge-teeth absent or rudimentary.
Cardinal process prominent.
Reniform impressions in dorsal valve.
(For muscular impressions see p. 501, Fig. 333.)
RANGE.--Silurian to Permian. Genus _Productus_ very
characteristic of the Carboniferous.
PRINCIPAL GENERA.--_Productus_, _Chonetes_, _Strophalosia_,
_Proboscidella_, _Aulosteges_.
Family. _Strophomenidae_
Shell very variable in shape; concavo-convex, plano-convex,
or biconvex; hinge line usually straight; frequently with an
area on each valve; foramen may or may not be present. Shell
structure near always punctate. Ventral valve usually furnished
with hinge-teeth; and dorsal valve with cardinal process.
Brachial supports completely absent or very rudimentary.
(For muscular impressions see p. 502, Fig. 334.)
RANGE.--Wholly Palaeozoic.
PRINCIPAL GENERA.--_Orthis_, with many sub-genera,
_Clitambonites_, _Skenidium_, _Strophomena_, _Orthothetes_,
_Leptaena_, _Stropheodonta_, _Plectambonites_.
Family. _Koninckinidae_
Shell plano-convex or concavo-convex. Brachial apparatus
composed of two lamellae spirally enrolled in the same plane, or
in the form of depressed cones, with the apices directed into
the ventral valve.
RANGE.--Silurian to Lias.
PRINCIPAL GENERA.--_Koninckina_, _Koninckella_, _Coelospira_,
_Davidsonia_.
Family. _Spiriferidae_
Shell biconvex. Brachial apparatus consisting essentially of two
descending calcareous lamellae which by spiral enrolment form a
pair of laterally-directed cones (Fig. 330).
RANGE.--Chiefly Palaeozoic, but a few forms pass up into the
Lias.
PRINCIPAL GENERA.--_Spirifera_, _Cyrtia_, _Uncites_, _Athyris_,
_Merista_.
Family. _Atrypidae_
Brachial apparatus consists of two descending calcareous
lamellae which bend outwards at the extremity of the crura and
are coiled into two spiral cones, the apices of which either
converge towards each other (_Glassia_) or towards the dorsal
valve (_Atrypa_, Fig. 332), or diverge towards the dorsal valve
(_Dayia_); shell structure impunctate.
RANGE.--Ordovician to Trias.
PRINCIPAL GENERA.--_Atrypa_, _Dayia_, _Glassia_.
Family. _Rhynchonellidae_
Shell biconvex, hinge line usually curved.
Beak of ventral valve incurved, with foramen.
Calcareous brachial supports reduced to a pair of short curved
crura.
The septa, dental and socket plates may be highly developed and
divide up the cavity of the shell into chambers (_Stenochisma_,
_Conchidium_).
Shell structure fibrous, rarely punctate; muscular impressions
as in _Terebratulidae_.
RANGE.--Ordovician to Recent: majority of the genera are
Palaeozoic.
PRINCIPAL GENERA.--_Rhynchonella_ (Fig. 327), _Stenochisma_,
_Stricklandia_, _Conchidium_.
Family. _Terebratulidae_
Shell structure punctate.
Arms supported by a calcareous loop, usually bent back on itself.
(For muscular impressions see p. 502, Figs. 328, 329.)
Beak of ventral valve perforated by foramen, furnished with
deltidium.
RANGE.--Devonian to Recent; maximum development in Mesozoic
times.
PRINCIPAL GENERA.--_Terebratula_, _Terebratulina_, _Waldheimia_,
_Terebratella_, _Kingena_, _Magas_, _Centronella_.
Family. _Argiopidae_
Large foramen for passage of pedicle. Marginal septa present
in both valves. Calcareous brachial loop follows margin of
shell and is more or less fused with the septa. Shell structure
punctate.
RANGE.--Jurassic to Recent.
PRINCIPAL GENERA.--_Argiope_, _Cistella_.
Family. _Stringocephalidae_
Shell subcircular, punctate. Cardinal process highly developed,
bifid. Brachial apparatus composed of two calcareous free
lamellae, prolonged at first downwards, then bent back, upwards
and outwards to run parallel to margin of shell and to unite in
front, thus constituting a wide loop.
RANGE.--Silurian and Devonian.
SOLE GENUS.--_Stringocephalus_.
Family. _Thecidiidae_
Shell usually fixed by beak of ventral valve, plano-convex.
Sub-cardinal apophysis in ventral valve for attachment of
occlusors. Marginal septa in dorsal valve. Calcareous brachial
loop more or less fused with shell, and with calcareous spicules
of mantle. Shell structure: inner layer fibrous, outer layer
tubulated.
RANGE.--Carboniferous to Recent.
PRINCIPAL GENERA.--_Thecidium_, _Oldhamina_.
STRATIGRAPHICAL DISTRIBUTION OF BRACHIOPODA
It is remarkable that some of the earliest types of Brachiopoda exist
generically unchanged at the present day. Such are _Lingula_, ranging
from the Cambrian; _Discina_ and _Crania_, ranging from the Ordovician;
and amongst the hinged forms _Terebratula_ from the Devonian, and
_Rhynchonella_ from the Ordovician.
In the lowest Cambrian (Olenellus beds) the most important genera
are _Linnarssonia_ and _Kutorgina_. The hinged forms appear in the
Cambrian, being represented by _Orthis_; but the majority in this
formation belong to the Ecardines. _Lingula_, _Lingulella_, and
_Obolella_ are characteristic.
In the Ordovician many new genera of the Testicardines make
their appearance, such as _Strophomena_, _Leptaena_, _Atrypa_,
_Rhynchonella_, _Clitambonites_, etc., but the extraordinary abundance
and variety of _Orthis_ is most remarkable. The Ecardines are
reinforced by such forms as _Trematis_ and _Siphonotreta_. It is,
however, in the Silurian that the Testicardinate Brachiopoda attain
their maximum, for in addition to a great development of species
amongst the older forms, a host of new genera for the first time occur
here (_Spirifera_, _Athyris_, _Conchidium_, _Stricklandia_, _Chonetes_,
_Cyrtia_, etc.); and the _Trimerellidae_ are especially characteristic
of the Wenlock.
With the commencement of Devonian times many species and genera
become extinct, but new forms come in (_Terebratula_, _Orthothetes_,
_Productus_, etc.), and some genera are wholly confined to this
formation (_Uncites_, _Stringocephalus_). The Carboniferous is
marked by the maximum development of _Productus_ and _Spirifera_;
_Orthothetes_, _Stenochisma_, and _Athyris_ are also abundant, but
there is a considerable extinction of the older genera and species, and
a great diminution in the number of individuals and species of those
that persist.
A further reduction occurs in the Permian, where the most important
genera are _Productus_, _Strophalosia_, and _Stenochisma_; but
_Aulosteges_ is a new form peculiar to this period. In the Trias a new
era commences; the principal families and genera of the older rocks
disappear entirely; a few spire-bearing genera persist (_Spiriferina_,
_Athyris_), and the genus _Koninckina_ is restricted to this formation.
The enormous development of species of the _Terebratulidae_ and
_Rhynchonellidae_ is the most noticeable feature in Jurassic times; and
a few ancient types linger on into the Lias (_Spiriferina_, _Suessia_,
a sub-genus of _Spirifera_); _Koninckella_ here occurs.
The Cretaceous Brachiopoda are closely allied to the Jurassic; _Magas_
and _Lyra_ are peculiar to the period, and the _Terebratulidae_ and
_Rhynchonellidae_ are very abundant, together with the Ecardinate genus
_Crania_.
With the commencement of Tertiary times the Brachiopoda have lost their
geological importance, and have dwindled down into an insignificant
proportion of the whole Invertebrate fauna.
* * * * *
The distribution of the Brachiopoda in past time is shown in the
following table:--
+------------------------------------+-----------------------+-----------+-------+
| | Palaeozoic | Mesozoic | |
| | | | | | C | | | | | | |
| | | | | | a | | | | | | |
| | | | | | r | | | | | | |
| | | O | | | b | | | | C | | |
| | | r | | | o | | | | r | | |
| | C | d | S | D | n | | | J | e | T | |
| | a | o | i | e | i | P | | u | t | e | |
| | m | v | l | v | f | e | | r | a | r | R |
| | b | i | u | o | e | r | T | a | c | t | e |
| | r | c | r | n | r | m | r | s | e | i | c |
| | i | i | i | i | o | i | i | s | o | a | e |
| | a | a | a | a | u | a | a | i | u | r | n |
| | n | n | n | n | s | n | s | c | s | y | t |
| ECARDINES +---+---+---+---+---+---+---+---+---+---+---+
| Lingulidae Lingula |___|___|___|___|___|___|___|___|___|___|___|
| Lingulella |___| | | | | | | | | | |
| Obolidae Obolus | |___|___| | | | | | | | |
| Obolella |___|___| | | | | | | | | |
| Kutorgina |___|___| | | | | | | | | |
| Linnarssonia |___| | | | | | | | | | |
| Trematis | |___|___| | | | | | | | |
| Siphonotreta | |___|___| | | | | | | | |
| Acrotreta | |___| | | | | | | | | |
| Discinidae Discina | |___|___|___|___|___|___|___|___|___|___|
| Craniidae Crania | |___|___|___|___|___|___|___|___|___|___|
| Trimerellidae Trimerella | | |___| | | | | | | | |
| Dinobolus | |___| | | | | | | | | |
| | | | | | | | | | | | |
| TESTICARDINES | | | | | | | | | | | |
| Productidae Productus | | | |___|___|___| | | | | |
| Chonetes | | |___|___|___| | | | | | |
| Strophalosia | | | |___|___|___| | | | | |
| Strophomenidae Orthis |___|___|___|___|___| | | | | | |
| Skenidium | |___|___| | | | | | | | |
| Clitambonites | |___| | | | | | | | | |
| Strophomena | |___|___| | | | | | | | |
| Stropheodonta | |___|___|___| | | | | | | |
| Leptaena | |___|___|___|___| | | | | | |
| Orthothetes | | | |___|___|___| | | | | |
| Davidsonia | | | |___| | | | | | | |
| Koninckinidae Koninckina | | | | | | |___| | | | |
| Koninckella | | | | | | | |___| | | |
| Spiriferidae Spirifera | | |___|___|___|___| | | | | |
| Spiriferina | | | |___|___|___|___|___| | | |
| Cyrtia | | |___|___|___| | | | | | |
| Syringothyris | | | | |___| | | | | | |
| Uncites | | | |___| | | | | | | |
| Athyris | | |___|___|___|___|___| | | | |
| Merista | | |___|___| | | | | | | |
| Retzia | | |___|___|___|___|___| | | | |
| Atrypidae Atrypa | |___|___|___|___|___|___| | | | |
| Dayia | | |___| | | | | | | | |
| Coelospira | | |___| | | | | | | | |
| Rhynchonellidae Rhynchonella | |___|___|___|___|___|___|___|___|___|___|
| Stenochisma | | | |___|___|___| | | | | |
| Stricklandia | | |___| | | | | | | | |
| Conchidium | | |___|___| | | | | | | |
| Terebratulidae Terebratula | | | |___|___|___|___|___|___|___|___|
| Terebratulina | | | | | | | |___|___|___|___|
| Waldheimia | | | | | | | |___|___|___|___|
| Terebratella | | | | | | | |___|___|___|___|
| Kingena | | | | | | | |___|___| | |
| Magas | | | | | | | | |___| | |
| Centronella | | |___|___|___| | | | | | |
| Argiopidae Argiope | | | | | | | |___|___|___|___|
| Cistella | | | | | | | |___|___|___|___|
| Stringocephalidae Stringocephalus | | | |___| | | | | | | |
| Thecidiidae Thecidium | | | | | | |___|___|___|___|___|
| Oldhamina | | | | |___| | | | | | |
| | | | | | | | | | | | |
+------------------------------------+---+---+---+---+---+---+---+---+---+---+---+
PHYLOGENY AND ONTOGENY
Wherever successive stages in the life history of an individual
resemble in important anatomical features the adult individuals of
other species occurring in successive members of a stratigraphical
series, the development of the individual may be regarded as an epitome
of the development of the species; it also generally throws light on
the origin and relationships of allied genera and families.
In the case of the fossil Brachiopoda comparatively little work has yet
been done in tracing their ontogeny or phylogeny, though the abundance,
variety, and excellent state of preservation of the extinct species
offer a promising field for investigation. It is to Dr. C. E. Beecher
and other recent American palaeontologists that we owe our advance in
this branch of the subject.
In the first place, in about forty genera, representing nearly all the
leading families of the group, the important fact has been established
of the presence of a common form of embryonic shell, termed the
“protegulum,” which is “semicircular or semielliptical in shape with a
straight or arcuate hinge line and no hinge area” (Beecher).[431] Its
minute size and delicate texture cause its preservation to be rare, but
its impression is not uncommonly left on the beak of the adult shell.
The main features of this embryonic shell are exhibited in the adult
Lower Cambrian Brachiopod _Obolus_ (_Kutorgina_) _labradoricus_
(Billings); the sub-equal semielliptical valves have lines of growth
running concentrically and parallel to the margin of the shell, and
ending abruptly against the straight hinge line; and this indicates
that there has been no change in the outline and proportions of the
shell during its stages of growth, but only a general increase in size.
It is very significant that we have here a mature type possessing the
common embryonic characters of a host of widely separated genera, and
we may therefore regard it as the most primitive form known.
Many genera pass through this so-called “Paterina” stage either in
the case of both their valves, or more generally in the case of the
dorsal valve only; but modifications in the form of the protegulum
arise, which are due to the influence of accelerated growth, by
which features belonging to later stages become impressed on the
early embryonic shell. The most variable and specialised valve--the
ventral or pedicle valve naturally exhibits the effect of this
influence first and to the greatest extent. The Palaeozoic adult forms
of many species represent various pre-adult stages of the Mesozoic,
Tertiary, and Recent species, as is especially well shown in the genera
_Orbiculoidea_ and _Discinisca_.
In the Strophomenoid shells the protegulum in the dorsal valve is
usually normal, but in the ventral valve abbreviation of the hinge
and curvature of the hinge line are produced by acceleration of the
“Discinoid stage” in which a pedicle notch is present.
No marked variation has yet been noticed in the spire-bearing, or
Terebratuloid, or Rhynchonelloid genera.
The form of the shell and the amount of difference in shape and size of
the valves seem to be largely due to the length of the pedicle and its
inclination to the axis of the body, as evidenced by the development
of _Terebratulina_. A series showing progressive dissimilarity of the
two valves arising from these causes can be traced from _Lingula_ to
_Crania_. The greater alteration that takes place in the ventral valve
appears to be due to its position as lower and attached valve. If the
pedicle is short a transversely-expanded shell with long hinge line
results when the plane of the valves is vertical or ascending, but
when the latter is horizontal a Discinoid form is found. This mode of
attachment is often accompanied by a more or less plainly developed
radial symmetry. Shells with long pedicles, on the other hand, are
usually longer than wide.
The character of the pedicle-opening is of great significance from
an evolutional and classificatory point of view, for the successive
stages through which it passes in embryonic growth are chronologically
paralleled by different genera, and are likewise accompanied by the
successive acquisition of other important anatomical characters, as
has been shown by Beecher and others. The first and simplest type of
pedicle opening is in shells with a posterior gaping of the valves,
where the pedicle protrudes freely between them in a line with the
axis, and the opening is shared by both valves, though generally
to a greater extent by the ventral valve. _Paterina_ (_= Obolus
labradoricus_) and _Lingula_ furnish examples of this type. In the
second type the pedicle opening is restricted to the ventral valve,
and the direction of the pedicle makes a right angle with the plane
of the valves; in the lower forms the pedicle lies in a slit or sinus
(_Trematidae_), but by further specialisation it becomes enclosed by
shell growth so as to lie within the periphery, and finally becomes
sub-central in some genera (_Discinidae_). The third type shows the
pedicle opening confined to the ventral valve and sub-marginal. A
pseudo-deltidium may preserve the original opening (_Clitambonites_);
or this shelly plate may become worn away or reabsorbed in the adult
so that the deltidial fissure through which the pedicle passes remains
quite open (_Orthidae_). In the fourth type the incipient stage marks
a return to the simple conditions of the first type; but ultimately
a pair of deltidial plates develop, and may completely limit the
pedicle opening below. Examples of this type are _Spirifera_ and
_Rhynchonella_. By means of these four types the Brachiopods have been
divided into four Orders: the _Atremata_ (type i.); the _Neotremata_
(type ii.); the _Protremata_ (type iii.); and the _Telotremata_ (type
iv.).
The _Telotremata_ were the last to appear, but the four types of
pedicle-opening with the various forms of calcareous brachial apparatus
were in existence in the Bala period of the Ordovician.
As _Paterina_ is the most primitive form of all, we may place it at
the root of the phylogenetic tree. From it sprang the _Atremata_,
which gave off the _Neotremata_ and _Protremata_; the most primitive
_Neotremata_ seem to be the _Trematidae_, while the connecting
link between the _Protremata_ and _Atremata_ is furnished by the
_Kutorginidae_. From the genus _Conchidium_ and its allies we may see
how the _Rhynchonellidae_ ushered in the _Telotremata_ as an offshoot
from the _Protremata_. The _Telotremata_ subsequently gave off two
main branches, which became specialised with the loop-bearing and
spire-bearing forms respectively.
The evolution and mutual relationships of genera have been indicated
with much probability by Hall, Clarke, and others. The Obolelloid
type may be connected with the Linguloid by means of _Lingulella_
and _Linyulepis_, while in _Lingula_ itself we find the point of
divergence for the ancestors of _Trimerella_, and for a line of
variation culminating in _Dignomia_. The Palaeozoic Rhynchonelloids
branched off at an early period from the same stock as _Orthis_, and
are connecting links between this genus and Mesozoic Rhynchonellae;
and a whole series of genera exhibit intermediate stages of structure
between the Rhynchonelloid and Pentameroid groups. The Terebratuloids
can be traced back to the primitive type _Renssoellaria_; and amongst
spire-bearing forms, the protean genus _Spirifera_ can be split up into
groups of species which diverge along lines tending to forms no longer
congeneric. When we come to deal with specific differences we find
frequently such a host of intermediate varieties that the separation of
many species, as in the case of Mesozoic Terebratulae, is to a large
extent arbitrary and artificial.
INDEX
References to figures are printed in thick type (=248=, =197=);
to systematic position, in italics (_391_, _430_)
_Abralia_, _391_
Absorption of internal portions of shell, 259
Abyssal Mollusca, 374
_Acanthinula_, _441_
_Acanthoceras_, _399_
_Acanthochiton_, =403=, _403_
_Acanthodoris_, _434_
_Acanthopleura_, _403_;
eyes, =188=
_Acavus_, 303, =304=, 335, _441_
_Acera_, 245, _430_
_Achatina_, 278, 328–337, =333=, _442_, =443=;
jaw, =211=;
food, 33;
size of egg, 124;
_A. fulica_, 279
_Achatinella_, 278, =326=, 327, _443_;
radula, =234=;
musical sounds, 51
_Achatinelloides_, 332
_Acicula_, 287, 296, _414_
_Acmaea_, _405_;
radula, 227
_Acme_, _414_
_Acmella_, 314, _415_
_Acroptychia_, 336, _414_
_Acrotreta_, _504_, 508
_Actaeon_, 250, 427, =428=, _429_;
radula, 217, 230;
streptoneurous, 203 n.
_Actaeonella_, _430_
_Actaeonia_, _432_
_Actaeonina_, 250, _429_
_Actinoceras_, _394_
_Actinodonta_, _447_
_Acusta_, 306, 316, 318, _441_
_Adacna_, =12=, 297, _455_
_Adalaria_, _434_
_Adamsiella_, _414_
_Addisonia_, _412_
_Adelphoceras_, _395_
_Adeorbis_, _416_
_Admete_, _426_
_Aegires_, _434_
_Aegista_, 305, 316, _441_
_Aegoceras_, _398_
_Aeolis_, =10=, =152=, _432_;
radula, 217, =229=;
stinging cells, 65;
mimicked by _Sagartia_, 68;
warning coloration, 72
_Aerope_, 328, 333, _440_;
radula, 215;
habits, 54
Aestivation, 25
_Aetheria_, 328–336, _452_;
variation, 92
_Africarion_, 333, _440_
_Agaronia_, _426_
Age of snails, 39
Aglossa, 7
Agnatha, habits, 51
_Akiodoris_, _434_
_Alaba_, _415_
_Alaria_, _418_
_Alariopsis_, _420_
_Albersia_, 320
Albino varieties, 87
_Alcadia_, 348–351, _410_
_Alderia_, _432_
_Alexia_, _439_
_Alicia_, _459_
_Allognathus_, _441_
_Allopagus_, _452_
Alloposidae, _384_
_Alvania_, _415_
_Alycaeus_, 266, 302 f., 309, 319, _414_
_Amalia_, _440_
_Amalthea_, 78
_Amaltheus_, _398_
_Amastra_, _443_
_Amaura_, _411_
_Amberleya_, _409_
_Ambonychia_, _449_
_Amicula_, _404_
_Ammonites_, 247, =393=, =398=, _398_;
sutures, =396=;
aptychus, =397=
Ammonoidea, _396_ f.
_Amnicola_, 325, _415_
_Amoria_, radula, 222
_Ampelita_, 335, _442_
_Amphibola_, 10, =18=, _439_;
breathing, 151;
radula, 236
_Amphibulimus_, 352, _442_;
radula, 233
_Amphidoxa_, 358
_Amphidromus_, 301, 305, 317, =310=, 359, _442_;
radula, 233
Amphineura, 8, _400_;
breathing organs, 154, 168;
nervous system, =203=;
genitalia, 145
_Amphipeplea_, _439_
_Amphiperas_, _419_
_Amphisphyra_, _430_
_Amphissa_, _423_
_Amphitretus_, =383=
_Ampullaria_, 17, _416_;
self-burial, 42;
spawn, =125=;
breathing organs, 151, =158=;
jaws, =212=;
shell, =249=, 263;
operculum, =268=;
distribution, 294, 320, 322, 343, 359
_Ampullarina_, 302, _439_
_Ampullina_, _411_
_Amussium_, _450_
_Amycla_, _423_
_Anabathron_, _415_
_Anachis_, _423_
_Anadenus_, 24, _441_
Anal glands, 241
Anal siphon, 164, 173
_Anastomopsis_, _442_
_Anatina_, 274, 275, _459_
Anatinacea, _458_;
gills, 167
_Anaulus_, _414_
_Anchistoma_, 293, 296
_Ancilla_, 267, _426_
_Ancillina_, _426_
_Ancistrochirus_, _391_
_Ancistromesus_, _405_
_Ancistroteuthis_, _391_
_Ancula_, _434_;
radula, 229, 230;
warning coloration, 72
_Anculotus_, _417_
_Ancyloceras_, 247, _399_
_Ancylus_, 19, _439_;
breathing, 162;
hibernating, 27;
radula, =235=
_Aneitea_, 325, _443_
_Angitrema_, 340, _417_
_Anisocardia_, _451_
_Anodonta_, 259, 341, _452_;
shower of, 47;
variation, 92;
_Glochidium_, =147=;
gill, =167=;
otocyst, =197=;
nervous system, =206=;
hinge, 274;
_A. anatina_, 24;
distribution, 282
_Anodontopsis_, _451_
_Anoglypta_, 325, _441_
_Anomia_, =257=, _448_, 464;
intestine, 241;
byssus hole, =262=;
hearing, 196
Anomiacea, _448_
_Anoplophora_, _451_
_Anostoma_, =248=, 266, 356, 358, _442_;
aperture, =63=
_Anthracosia_, _451_
_Anura_, _424_
Anus, 209, 241
_Apera_, 334, _440_
_Aperostoma_, 344, _414_
_Aphanotrochus_, _408_
_Aphelodoris_, radula, 230
_Apicalia_, _422_
Aplacophora, 9, _404_;
radula, 228
_Aplecta_, 354, _439_
_Aplustrum_, =245=, =428=, _430_;
radula, 230
_Aplysia_, 245, =428=, _431_;
stomach, 239;
purple fluid, 65
_Aplysioidea_, _430_
_Aporrhais_, _418_;
radula, 215
_Apricardia_, _455_
Aptychus, =397=
_Aptyxiella_, _417_
_Aptyxis_, _424_
Aral Sea, _Limnaea_ from near, =84=;
_Cardium_ from, 91
_Arca_, =14=, 171, =273=, _448_;
eyes, =191=
Arcacea, _448_
Arcachon, oyster-parks at, 105
_Arcestes_, _397_
_Archidoris_, =434=, _434_;
protective coloration, 73
_Architeuthis_, 378, =390=, _390_;
sucker, =381=
_Arcomya_, _458_
_Arconaia_, 307, _452_
Arctic shells, colour of, 86
_Arcuella_, _422_
_Argiope_, =470=, 472, 479, _487_;
parasite of, 485;
distribution, 486;
fossil, 501, _506_, 508
Argiopidae, _506_, 508
_Argobuccinum_, _420_
_Argonauta_, =383=, _383_;
egg-laying, 127;
hectocotylised arm, 137;
radula, 236
_Arinia_, _413_
_Ariolimax_, _441_, 341;
radula, 233
_Arion_, _440_;
shell, 175, 245, 246;
hardier than _Helix_, 24;
voracity, 30 f.;
egg-laying, 42 f.;
protective coloration, 70;
pulmonary orifice, 160;
food, 179;
smell, 193 f.;
radula, 233;
distribution, 285
_Arionta_, =341=, 353, _441_
_Ariophanta_, 301, =308=, 309, 316, _440_;
protective coloration, 70
Aristotle, on modified arm of polypus, 138
_Artemis_, _454_
_Arthuria_, _403_
_Asaphis_, _456_
_Ascoceras_, _394_
Ascoglossa, 11 n., _431_
Ashford, C., on pulsations of heart in _Helix_, 26;
on homing of _Helix_, 35;
on dart-sac, 143
_Asolene_, _416_
_Aspergillum_, 262, _459_
_Aspidelus_, 329, _440_
_Aspidoceras_, _399_
_Assiminea_, _415_
_Astarte_, _451_
_Asthenothaerus_, _459_
_Astralium_, _409_
_Athoracophorus_, _443_--see _Janella_
_Athyris_, 499, 500, _505_;
stratigraphical distribution, 507, 508
_Atilia_, _423_
_Atlanta_, 421, _422_;
foot, 200
_Atopocochlis_, 330, _441_
Atremata, 511
_Atretia_, distribution, 486, _487_
_Atrypa_, 501, =502=, _505_;
stratigraphical distribution, 507, 508
Atrypidae, 501, 505, 508
_Aturia_, 393, _395_
_Atys_, =428=, _430_
Aucapitaine, H., on tenacity of life, 38
_Aucella_, _449_
_Aulopoma_, 157, 304, _414_;
operculum, =269=
_Aulosteges_, _504_;
stratigraphical distribution, 507
_Auricula_, =439=, _439_
_Auriculella_, 327, _443_
Auriculidae, 17, =18=, =260=, =439=, _439_;
lung, 160;
eyes, 186;
radula, 235
_Austenia_, 301, 304, _440_
_Avellana_, _430_
_Avicula_, 254, 258, =449=, _449_;
eyes, 190;
genital orifice, 242;
_A. margaritifera_, 100
_Aviculopecten_, _450_
_Aviculopinna_, _449_
_Axinus_, _452_
_Azeca_, _442_
Azygobranchiata, 155, 407
_Babinka_, _447_
_Bactrites_, _395_
_Baculites_, _399_
_Baikalia_, 290, _415_
Baird, Mr., on the British Museum snail, 37
_Balea_, _442_;
_B. perversa_, 24, 41
Baltic, fauna of the, 12, 83, 366
_Bankivia_, _408_
_Barbatia_, _448_
_Barleeia_, _415_
Barnacle, Rev. H. G., on musical sounds, produced by Mollusca, 51
Barometers, snails as, 50
_Bartlettia_, _452_
_Basilissa_, 376, _408_
Basommatophora, 11, 19, 181, _438_
_Basterotia_, _451_
Bateson, W., on variation in _Cardium_, 91;
on hearing in _Anomia_, 196
_Bathmoceras_, _395_
_Bathydoris_, _433_
_Bathyteuthis_, _390_
_Batissa_, 320, _453_
_Beddomea_, 304
Beecher on phylogeny, 509
Beetles, prey on Mollusca, 58
_Bela_, _426_;
radula, =219=
_Belemnites_, 380
Belemnitidae, _387_
_Belemnosepia_, _390_
_Bellerophon_, =266=, _407_
_Belopetra_, 380
Belopteridae, _388_
_Belosepia_, 386, _388_
_Beloteuthis_, _390_
_Bembix_, 376, _408_
_Benedictia_, 290, _415_
_Benthobia_, 377
_Benthodolium_, 377
_Berendtia_, _441_
Beudant, experiments on Mollusca, 12
Bideford Bridge and mussels, 117
Binney, Dr., on epiphragm, 28
_Binneya_, 341, _441_
_Biradiolites_, _456_
Birds, devour Mollusca, 56 f.
_Bithynella_, 289, 293, _415_
_Bithynia_, 336, 342, _415_;
stomach, 239;
habitat, 25
_Bittium_, _416_
_Blaesospira_, 346, 351
_Blandiella_, 16, _414_
_Blanfordia_, _414_
Blind Mollusca, 185
Blood, 171
Bodö, land Mollusca, 24
Boeuf and French oysters, 107
_Bolma_, _409_
_Boltenia_, _346_
_Boreofusus_, radula, 221
_Bornella_, _433_;
stomach, 239
_Borsonia_, _426_
_Borus_, 356–358, _441_
_Bourcieria_, 357, _410_
_Bourguetia_, _417_
_Bourguignatia_, 332
Bouvier--_see_ Fischer
_Boysia_, 302, _442_
Brachial apparatus, types of, 500
Brachiopoda, fossil, limestone formed of, 492;
shell, 493, 497;
muscle scars on, 494, 501;
platform, 495;
synopsis of families, 503;
stratigraphical distribution, 506;
phylogeny and ontogeny, 509;
Orders, 511
Brachiopoda, recent, 463;
historical account of, 464;
shell, 465;
body, 469;
digestive system, 471;
body cavity, 472;
heart, 473;
excretory organs, 474;
muscles, 475;
nervous system, 478;
reproductive system, 478;
embryology, 479;
habits, 482;
distribution, 484;
classification, 487;
affinities, 487
_Brachytrema_, _417_
Brackish-water species, 14
Branchiae, 151, 153, 164
Branchial siphon, 155, 164, 173
Braun, on self-impregnation, 44
Breathing organs--_see_ Respiration, Branchiae
_Brechites_, _459_
Breeding, periodicity in, 129
_Broderipia_, _408_
_Brotia_, 305
_Brownia_, 133
_Buccinanops_, _423_
_Buccinopsis_, _424_;
radula, 221, 222;
egg-laying, 128
_Buccinum_, =6=, _424_;
radula, 217;
monstrosity, =251=;
breeding, 129;
osphradium, =195=;
spawn, =126=
_Buliminus_, 24, 278, 285, =295= f., 316, 331, 339, _442_;
protective habits, 70;
_B. pallidior_, 38
_Bulimulus_, 278, 334, 339–359, _442_;
jaw, =211=, 233;
radula, 233;
variation, 87
_Bulimus_, 278, 342–359, =355=, _441_;
radula, 233;
egg, =124=
_Bulinus_--see _Isidora_
_Bulla_, 428, _430_
_Bullia_, =155=, _423_;
habits, 192;
foot, 198;
radula, 221
Bulloidea, _429_
Burrowing Mollusca, 446
Burying propensities of Mollusca, 27, 41
_Busycon_, _424_;
money made from, 97;
egg-capsules, =125=--see _Fulgur_
Butterell, Mr., on habits of _Testacella_, 52
_Byssocardium_, _455_
Byssus gland, 201
_Cadlina_, _434_
_Cadoceras_, =393=
_Cadulus_, 376, _445_
_Caecilianella_, _442_;
habitat, 48;
eyes, 186
_Calcarella_, 133
California, land Mollusca, 280
_Calliostoma_, _408_;
jaws, =212=
_Callistochiton_, _403_
_Callochiton_, _403_
_Callogaza_, _408_
_Callonia_, _442_
_Callopoma_, _409_
_Calma_, protective coloration, 74
_Calybium_, _410_
_Calycia_, 320, _442_
_Calycidoris_, _434_
_Calyptraea_, =248=, _412_
_Camaena_, 305, 306, 315, =316=, _441_
Cambrian, Mollusca of the, 2
_Camitia_, _409_
_Campaspe_, _433_
_Camptoceras_, =302=
_Camptonyx_, 278, =302=, _439_
_Campylaea_, 285, 289 f., =293=, _441_
Canal, 155
_Cancellaria_, _426_
_Canidia_, 16, 305, _423_
Cannibalism in snails and slugs, 32, 33
_Cantharidus_, _408_
_Cantharus_, 275;
radula, =222=
_Caprina_, _456_
_Caprotina_, _456_
_Capulus_, _412_
_Caracolus_, =347=-351, _441_
_Carbonicola_, _451_
Cardiacea, _454_
_Cardiapoda_, _421_
_Cardilia_, _454_
Cardinal plate, 500
Cardinal process, 497, 501
_Cardinalia_, _408_
_Cardinia_, _451_
_Cardita_, =273=, _451_
_Carditella_, _451_
_Carditopsis_, _451_
_Cardium_, =6=, =273=, =455=, _455_;
_C. edule_, =12=, =164=;
modifications, 12;
variation, 84, =91=;
nervous system, 207;
distribution, 292, 297
_Carelia_, 327, _443_
_Carinaria_, =9=, =422=, _422_;
foot, 200
_Carinifex_, _439_
_Carolia_, _448_
_Cartusiana_, 296
_Carychium_, 18, _439_
_Caryodes_, 325, 359, _441_
_Casella_, radula, 230
_Caspia_, 12, 297
Caspian Sea, fauna, 12, 297
_Cassidaria_, _420_
_Cassidula_, =18=, 278, =439=, _439_
_Cassis_, 255, _420_;
radula, =223=
_Castalia_, 344, _452_
_Cataulus_, 157, 266, 304, _414_
Caterpillars mimicking _Clausilia_, 68
_Cathaica_, 316, _441_
_Catinella_, _443_
_Cavolinia_, 158, _436_;
eyes, 186
_Cecina_, _414_
_Cenia_, _432_;
breathing, 152
_Centrodoris_, _434_;
radula, 230
_Centronella_, 499, _506_, 508
Cephalopoda, 378 f.;
defined, 5;
ink, 65;
egg-laying, 127;
embryo, =133=;
branchiae, 168;
osphradium, 195;
foot, 200;
nervous system, 206;
jaws, 213;
radula, 236
_Cepolis_, 349–351, _441_
_Cerastoma_, _423_
_Cerastus_, 331, _441_
Cerata of Nudibranchs, 71, 159
_Ceratites_, _397_, =398=;
suture, =396=
_Ceratodes_, 357, _416_
_Ceres_, =21=, 354, _410_
_Ceritella_, _417_
_Cerithidea_, 260, _417_;
_C. obtusa_, breathing, 152
_Cerithiopsis_, _417_
_Cerithium_, =16=, _416_
_Ceromya_, _458_
_Chaetoderma_, =404=, _404_;
breathing organs, =154=;
nervous system, =203=;
radula, 217, 228
_Chaetopleura_, _403_
_Chama_, 257, 272, 446, _455_
_Chamostrea_, _458_
Changes in environment, effect of, 83 f.
Chank-shell, fishery of, 100
_Charis_, 324, _442_
_Charopa_, 319, 323–327, _441_
_Chascax_, _424_
_Chelinodura_, _430_
_Chelotropis_, 133
_Chenopus_, _418_
Chilidium, 498
_Chilina_, 19, _343_, 358
Chilinidae, _439_;
radula, 236
_Chilotrema_, _441_
China, use of shells in, 101
_Chiropteron_, 133
_Chiroteuthis_, 385, _391_
_Chiton_, =8=, =153=, _403_;
egg-laying, 126;
breathing organs, 153 f.;
eyes, =188=;
osphradium, 195;
radula, =228=;
nervous system, =203=;
valves, =401=, =402=;
girdle, =403=
_Chitonellus_, =404=, _404_;
valves, =401=
_Chittya_, 16, 348, 351, _414_
_Chlamydephorus_, 333, _440_
_Chlamydoconcha_, 175, 245, _453_
_Chlamys_, _450_
_Chloritis_, 306, 311, 319–324, _441_
_Chlorostoma_, _408_
_Chlorostracia_, 307
_Choanomphalus_, 250, 290, _439_
Chondrophora, _389_
_Chondropoma_, 346–355, =348=, _414_
_Chondrula_, 285, =295=, 296, _442_
_Choneplax_, _404_
_Chonetes_, _504_;
stratigraphical distribution, 507, 508
_Choristes_, _420_
_Choristoceras_, _398_
_Chorus_, _423_
_Chromodoris_, _434_;
jaws, =212=;
radula, 230
_Chrysallida_, _422_
_Chrysodomus_, _423_
_Chrysostoma_, _409_
_Cingula_, _415_
_Cingulina_, _422_
_Cionella_, _442_
_Circe_, _454_, =458=
Circulatory system, 169
_Circulus_, _408_
Circumpolar species, 287
_Cirrhoteuthis_, 381, =382=
_Cistella_, 467, =470=, 472, 475, 476, 479, 480, _487_;
larvae, =481=, 483;
parasite of, 485;
distribution, 486;
fossil, _506_, 508
_Cistopus_, _385_
_Cistula_, 349, 351, 355, _414_
Cladohepatica, _432_
_Clanculus_, _408_
Classification, 5, 8;
of Gasteropoda, 8, 11
_Clathurella_, _426_
_Clausilia_, =442=, _442_;
mimicked by caterpillars, 68;
monstrosity, 251;
distribution, 285 f., =294=, 305–318, 332, 339–356;
_C. rugosa_, 24;
_scalaris_, 278
_Clavagella_, 262, _459_
_Clavator_, 335, 359, _441_
_Clavatula_, _426_
_Clavella_, _424_
_Claviger_, 329, _417_
_Clea_, =16=, 305, _423_
_Clementia_, _454_
_Cleodora_, =436=, _436_
_Cleopatra_, 294, 328, 331, 336, _416_
Clessin, on duration of life, 39
_Clessinia_, 12, 297
_Clio_, =436=, _436_
_Cliona_, enemy of oysters, 112
_Clione_, 158, _438_
_Clionopsis_, _437_
_Clitambonites_, 498, _505_;
stratigraphical distribution, 507, 508, 511
_Clithon_, 327, _410_
_Clydonites_, _398_
_Clymenia_, _397_
_Clypidella_, _406_
_Cocculina_, _408_
_Cochlicella acuta_, 278
_Cochliolepas_, 77
_Cochloceras_, _398_
_Cochlodésma_, _459_
_Cochlostyla_, 124, 278, =313=, 315, _441_
Cockles, use of, 101, 118
_Coecum_, 247, =260=, _417_, =418=
_Coeliaxis_, 334, _442_;
habitat, 49
_Coelocentrum_, =353=, _442_
_Coelospira_, _505_, 508
Cold winter, effect on oysters, 112;
on mussels, 116
Collinge, W. E., on growth and burial of shells, 41
_Collisella_, _405_
_Collisellina_, _405_;
radula, 227
_Collonia_, _409_
_Colobocephalus_, _430_
Colour of arctic shells, 86
_Colpodaspis_, _430_
_Columbarium_, _426_
_Columbella_, _423_;
radula, =222=
_Columbellaria_, _420_
_Columbellina_, _420_
_Columna_, 328, =330=, _443_
_Cominella_, =16=, _424_
Composition of shell, 252
_Concha_, 463
_Conchidium_, 497, =498=, 500, _505_;
stratigraphical distribution, 507, 508, 511
_Concholepas_, 267, _423_
_Conidea_, _423_
_Conocardium_, _455_
_Conorbis_, _426_
_Conus_, 247, 275, _426_;
poisonous bite, 65;
tooth, =66=;
shell, =69=, =255=, 260;
mimicked by _Strombus_, 69;
prices given for rare, 121;
spawn, =125=;
radula, 218, =220=;
operculum, =269=
_Cookia_, _409_
_Coptochilus_, 314, _414_
_Coralliophaga_, _451_
_Coralliophila_, 75, _423_
Coralliophilidae, radula, 216
_Corambe_, _434_
_Corasia_, 311, 319–321
_Corbicula_, 15, 288, 292 f., _453_
_Corbis_, _452_
_Corbula_, _456_
_Corilla_, 303
_Corona_, 27, _442_
_Coronaria_, =297=
_Coryda_, 346–351, _441_
_Coryphella_, _432_
_Cosmoceras_, _399_
Cowry used as money, 96
Coyote trapped by _Haliotis_, 57
_Cranchia_, _391_
Crania, 464, =467=, 468, 469, 471, 472, 473, 475, 476, =477=,
_487_;
distribution, 485;
fossil, 493, 494, _504_;
stratigraphical distribution, 506, 507, 508, 510
Craniidae, _487_, 496, _504_, 508
_Cranopsis_, =265=, _406_
_Craspedochiton_, _403_
_Craspedopoma_, 298, _414_
_Craspedostoma_, _408_
_Crassatella_, _451_
_Cratena_, _432_
Crawling of _Helix_, 45
_Cremnoconchus_, 16, 302, _413_
_Crenatula_, 75, _449_
_Crenella_, _449_
_Crenipecten_, _450_
_Crepidula_, =248=, 257, =412=, _412_;
parasitic, =78=
_Crepipatella_, =248=, _412_
_Creseis_, =436=, _436_;
eyes, 186
_Crimora_, _434_;
radula, 229
_Crioceras_, 247, =399=, _399_
_Cristigibba_, 311, 319, 320, _441_
_Crossostoma_, _408_
_Crucibulum_, =248=, _412_
_Cryptochiton_, 245, 371, 402, _404_
_Cryptochorda_, _425_
_Cryptoconchus_, _404_
_Cryptophthalmus_, _430_
_Cryptostracon_, 353, _441_
Ctenidia, 151--_see_ Branchiae
_Ctenopoma_, 346–351, _414_
_Cucullaea_, 274, _448_
_Cultellus_, _457_
_Cuma_, _423_
_Cumingia_, _453_
_Cuspidaria_, _459_;
branchiae, 168
_Cuvierina_, =436=, _436_
_Cyane_, _410_
_Cyathopoma_, =247=, 268, 314, 338, _414_
_Cyclas_, _453_;
veliger, =132=;
ova, 146;
otocyst, =197=;
_C. cornea_, thread-spinning, 29;
distribution, 282
_Cyclina_, _454_
Cyclobranchiata, 156
_Cyclocantha_, _409_
_Cyclomorpha_, _414_
_Cyclonassa_, _423_
_Cyclonema_, _409_
Cyclophoridae, origin, 21
_Cyclophorus_, 302, =306=-319, 329–334, 344, 352–358, _414_;
jaws, =212=;
radula, =21=
_Cyclostoma_, 328, 331–338, =414=, _414_;
stomach, 239;
vision, 184;
osphradium, 195;
nervous system, =205=;
_C. elegans_, 287, 288
Cyclostomatidae, origin, 21;
radula, 224;
gait, 199
_Cyclostrema_, _408_
_Cyclosurus_, =247=, 337, _414_
_Cyclotopsis_, 338, _414_
_Cyclotus_, 296, 319, 320, _414_
_Cylichna_, =428=, _430_;
radula, 215
_Cylindrella_, =247=, =260=, 278, 343–355, =348=, _442_;
monstrosity, 251, =252=
Cylindrellidae, radula, 233, =234=
_Cylindrites_, _430_
_Cylindrobulla_, _430_
_Cylindromitra_, _425_;
radula, 222
_Cymbium_, 255, 367, _425_;
radula, =221=
_Cymbulia_, _437_
_Cymbuliopsis_, _437_
_Cynodonta_, _424_
_Cyphoma_, _419_
_Cypraea_, =178=, _419_;
prices given for rare, 122;
mantle-lobes, 177, =178=;
radula, =224=;
shell, =255=, 260, =261=;
_C. moneta_, 96
_Cypraecassis_, _420_
_Cypraedia_, _419_
_Cypraeovula_, _419_
_Cyprimeria_, _454_
_Cyprina_, _451_
_Cyrena_, 15, _453_;
distribution, 285, 294
_Cyrenella_, _453_
_Cyrtia_, _505_;
stratigraphical distribution, 507, 508
_Cyrtoceras_, _394_
_Cyrtodaria_, _457_
_Cyrtodonta_, _452_
_Cyrtolites_, _407_
_Cyrtonotus_, _448_
_Cyrtotoma_, _414_
_Cysticopsis_, 346–351, _441_
_Cystiscus_, _425_
_Cystopelta_, 325, 326, _440_
_Cytherea_, =454=, _454_
_Dacrydium_, _449_
_Daedalochila_, _441_
Dall, W. H., quoted, 35;
on branchiae, 164
_Damayantia_, _440_
_Daphnella_, _426_
Darbyshire, R. D., on tenacity of life, 39
_Dardania_, _415_
Dart-sac, 142
_Daudebardia_, =289=, 292 f., _440_
_Davidsonia_, _505_, 508
_Dawsonella_, _410_
_Dayia_, _505_, 508
Decapoda, _385_ f.
Decollation, 260
Deep-sea Mollusca, 374
De Folin, experiment on _Cyclostoma_, 157
_Deianira_, _410_
Delage, experiments on otocysts, 197
_Delphinula_, _409_
Deltidium, 499
_Dendronotus_, _433_;
protective coloration, 72;
habits, 51
_Dentalium_, =6=, =444=, _445_;
used as money, 97;
veliger, =131=;
radula, =228=
_Dentellaria_, =350=-355, _441_;
aperture, =63=
Desert species, 25, 85
_Deshayesia_, _411_
_Desmoulea_, _423_
Development of fertilised ovum, 130 f.
_Dexiobranchaea_, _437_
_Diadema_, _414_
_Diala_, _415_
_Dialeuca_, _441_
_Diaphora_, 314
_Diaphorostoma_, _412_