ISOSPONDYLI
=THE Subclass Teleostei, or Bony Fishes.=—The fishes which still remain
for discussion constitute the great subclass or series of _Teleostei_
(τελεός, true; οστέον, bone), or bony fishes. They lack wholly or partly
the Ganoid traits, or show them only in the embryo. The tail is
slightly, if at all, heterocercal; the actinosts of the pectoral fins
are few and large, rarely over five in number, except among the eels;
the fulcra disappear; the air-bladder is no longer cellular, except in
very rare cases, nor does it assist in respiration. The optic nerves are
separate, one running to each eye without crossing; the skeleton is
almost entirely bony, the notochord usually disappearing entirely with
age; the valves in the arterial bulb are reduced in number, and the
spiral valve of the intestines disappears. Traces of each of the Ganoid
traits may persist somewhere in some group, but as a whole we see a
distinct specialization and a distinct movement toward the fish type,
with the loss of characters distinctive of sharks, Dipnoans, and
Ganoids. In a general way the skeleton of all Teleosts corresponds with
that of the striped bass (see Figs. 22, 23, Vol. I), and the visceral
anatomy is in all cases sufficiently like that of the sunfish (Fig. 16,
Vol. I).
The mesocoracoid or precoracoid arch, found in all Ganoids, persists in
the less specialized types of bony fishes, although no trace of it is
found in the perch-like forms. With all this, there is developed among
the bony fishes an infinite variety in details of structure. For this
reason the _Teleostei_ must be broken into many orders, and these orders
are very different in value and in degrees of distinctness, the various
groups being joined by numerous and puzzling intergradations.
=Order Isospondyli.=—Of the various subordinate groups of bony fishes,
there can be no question as to which is most primitive in structure, or
as to which stands nearest the orders of Ganoids. Earliest of the bony
fishes in geological time is the order of _Isospondyli_ (ἴσος, equal;
σπόνδυλος, vertebra), containing the allies, recent or fossil, of the
herring and the trout. This order contains those soft-rayed fishes in
which the ventral fins are abdominal, a mesocoracoid or precoracoid arch
is developed, and the anterior vertebræ are unmodified and essentially
similar to the others. The orbitosphenoid is present in all typical
forms. In certain forms of doubtful affinity (_Iniomi_) the mesocoracoid
is wanting or lost in degeneration. Through the _Isospondyli_ all the
families of fishes yet to be considered are apparently descended, their
ancestors being Ganoid fishes and, still farther back, the
Crossopterygians.
Woodward gives this definition of the _Isospondyli_: "Notochord varying
in persistence, the vertebral centra usually complete, but none
coalesced; tail homocercal, but hæmal supports not much expanded or
fused. Symplectic bone present, mandible simple, each dentary consisting
only of two elements (dentary and articulo-angular), with rare rudiments
of a splenoid on the inner side. Pectoral arch suspended from the
cranium; precoracoid (mesocoracoid) arch present; infraclavicular plates
wanting. Pelvic (ventral) fins abdominal. Scales ganoid only in the less
specialized families. In the living forms air-bladder connected with the
œsophagus in the adult; optic nerves decussating (without chiasma), and
intestine either wanting spiral valve or with an incomplete
representative of it."
=The Classification of the Bony Fishes.=—The classification of fishes
has been greatly complicated by the variety of names applied to groups
which are substantially but not quite identical one with another. The
difference in these schemes of classification lies in the point of view.
In all cases a single character must be brought to the front; such
characters never stand quite alone, and to lay emphasis on another
character is to make an alteration large or small in the name or in the
boundaries of a class or order. Thus the _Ostariophysi_ with the
_Isospondyli_, _Haplomi_, and a few minor groups make up the great
division of the _Abdominales_. These are fishes in which the ventral
fins are abdominal, that is, inserted backward, so that the pelvis is
free from the clavicle, the two sets of limbs being attached to
different parts of the skeleton. Most of the abdominal fishes are also
soft-rayed fishes, that is, without consecutive spines in the dorsal and
anal fins, and they show a number of other archaic peculiarities. The
Malacopterygians (μαλακός, soft; πτερύξ, fin) of Cuvier therefore
correspond very nearly to the _Abdominales_. But they are not quite the
same, as the spiny-rayed barracudas and mullets have abdominal ventrals,
and many unquestioned thoracic or jugular fishes, as the sea-snails and
brotulids, have lost, through degeneration, all of their fin-spines.
In nearly but not quite all of the Abdominal fishes the slender tube
connecting the air-bladder with the œsophagus persists through life.
This character defines Müller's order of _Physostomi_ (φυσός, bladder;
στόμα, mouth), as opposed to his _Physoclysti_ (φυσός, bladder;
κλεῖστός, closed), in which this tube is present in the embryo or larva
only. Thus the _Thoracices_ and _Jugulares_, or fishes having the
ventrals thoracic or jugular, together correspond almost exactly to the
Acanthopterygians, (ακανθα, spine; πτερύξ, fin), or spiny-rayed fishes
of Cuvier, or to the _Physoclysti_ of Müller. The Malacopterygians, the
_Abdominales_, and the _Physostomi_ are in the same way practically
identical groups. As the spiny-rayed fishes have mostly ctenoid scales,
and the soft-rayed fishes cycloid scales, the _Physostomi_ correspond
roughly to Agassiz's _Cycloidei_, and the _Physoclysti_ to his
_Ctenoidei_.
But in none of these cases is the correspondence perfectly exact, and in
any system of classification we must choose characters for primary
divisions so ancient and therefore so permanent as to leave no room for
exceptions. The extraordinary difficulty of doing this, with the
presence of most puzzling intergradations, has led Dr. Gill to suggest
that the great body of bony fishes, soft-rayed and spiny-rayed,
abdominal, thoracic, and jugular alike, be placed in a single great
order which he calls _Teleocephali_ (τελεός, perfect; κεφαλή, head). The
aberrant forms with defective skull and membrane-bones he would separate
as minor offshoots from this great mass with the name of separate
orders. But while the divisions of _Teleocephali_ are not strongly
differentiated, their distinctive characters are real, ancient, and
important, while those of the aberrant groups, called orders by Gill (as
_Plectognathi_, _Pediculati_, _Hemibranchii_), are relatively modern and
superficial, which is one reason why they are more easily defined. There
seems to us no special advantage in the retention of a central order
_Teleocephali_, from which the divergent branches are separated as
distinct orders.
While our knowledge of the osteology and embryology of most of the
families of fishes is very incomplete, it is evident that the
relationships of the groups cannot be shown in any linear series or by
any conceivable arrangement of orders and suborders. The living teleost
fishes have sprung from many lines of descent, their relationships are
extremely diverse, and their differences are of every possible degree of
value. The ordinary schemes have magnified the value of a few common
characters, at the same time neglecting other differences of equal
value. No system of arrangement which throws these fishes into large
groups can ever be definite or permanent.
=Relationships of Isospondyli.=—For our purposes we may divide the
physostomous fishes as understood by Müller into several orders, the
most primitive, the most generalized, and economically the most
important being the order of _Isospondyli_. This order contains those
bony fishes which have the anterior vertebræ unaltered (as distinguished
from the _Ostariophysi_), the skull relatively complete, or at least not
eel-like, the mesocoracoid typically developed, but atrophied in
deep-sea forms and finally lost, the orbitosphenoid present. In all the
species the ventral fins are abdominal and normally composed of more
than six rays; the air-duct is developed. The scales are chiefly cycloid
and the fins are without true spines. In many ways the order is more
primitive than _Nematognathi_, _Plectospondyli_, or _Apodes_. It is
certain that it began earlier in geological time than any of these. On
the other hand, the _Isospondyli_ are closely connected through the
_Berycoidei_ with the highly specialized fishes. The continuity of the
natural series is therefore interrupted by the interposition of the side
branches of Ostariophysans and eels before considering the _Haplomi_ and
the other transitional forms. The forms called _Iniomi_, which lack the
mesocoracoid and the orbitosphenoid, have been lately transferred to the
_Haplomi_ by Boulenger. This arrangement is probably a step in advance.
Ganoid traits are present in certain families of _Isospondyli_. Among
these are the gular plate (found in _Amia_ and the _Elopidæ_), doubtless
derived from the similar structure in earlier Ganoids; additional valves
in the arterial bulb in the cellular air-bladder of _Notopterus_ and
_Osteoglossum_, the spiral intestinal valve in _Chirocentridæ_, and the
ganoid scales of the extinct _Leptolepidæ_.
=The Clupeoidea.=—The _Isospondyli_ are divisible into numerous
families, which may be grouped roughly under three subdivisions,
_Clupeoidea_, the herring-like forms; the _Salmonoidea_, the trout-like
forms; and the _Iniomi_, or lantern-fishes, and their allies. The
last-named group should probably be removed from the order of
_Isospondyli_. In the _Clupeoidea_, the allies of the great family of
the herring, the shoulder-girdle is normally developed, retaining the
mesocoracoid arch on its inner edge, and through the post-temporal is
articulated above with the cranium. The fishes in this group lack the
adipose fin which is characteristic of most of the higher or salmon-like
families.
[Illustration:
FIG. 27.—_Leptolepis dubius_ Blainville, Lithographic Stone. (After
Woodward.)
]
=The Leptolepidæ.=—Most primitive of the _Isospondyli_ is the extinct
family of _Leptolepidæ_, closely allied to the Ganoid families of
_Pholidophoridæ_ and _Oligopleuridæ_. It is composed of graceful,
herring-like fishes, with the bones of the head thin but covered with
enamel, and the scales thin but firm and enameled on their free portion.
There are no fulcra and there is no lateral line. The vertebræ are well
developed, but always pierced by the notochord. The genera are
_Lycoptera_, _Leptolepis_, _Æthalion_, and _Thrissops_. In _Lycoptera_
of the Jurassic of China the vertebral centra are feebly developed, and
the dorsal fin short and posterior. In _Leptolepis_ the anal is short
and placed behind the dorsal. There are many species, mostly from the
Triassic and lithographic shales of Europe, one being found in the
Cretaceous. _Leptolepis coryphænoides_ and _Leptolepis dubius_ are among
the more common species. _Æthalion_ (_knorri_) differs in the form of
the jaws. In _Thrissops_ the anal fin is long and opposite the dorsal.
_Thrissops salmonea_ is found in the lithographic stone; _Thrissops
exigua_ in the Cretaceous. In all these early forms there is a hard
casque over the brain-cavity, as in the living types, _Amia_ and
_Osteoglossum_.
[Illustration:
FIG. 28.—Ten-pounder, _Elops saurus_ L. An ally of the earliest bony
fishes. Virginia.
]
[Illustration:
FIG. 29.—A primitive Herring-like fish, _Holcolepis lewesiensis_,
Mantell, restored. Family _Elopidæ_. English Chalk. (After
Woodward.)
]
=The Elopidæ.=—The family of _Elopidæ_ contains large fishes
herring-like in form and structure, but having a flat membrane-bone or
gular plate between the branches of the lower jaw, as in the Ganoid
genus _Amia_. The living species are few, abounding in the tropical
seas, important for their size and numbers, though not valued as
food-fishes save to those who, like the Hawaiians and Japanese, eat
fishes raw. These people prefer for that purpose the white-meated or
soft-fleshed forms like _Elops_ or _Scarus_ to those which yield a
better flavor when cooked.
The ten-pounder (_Elops saurus_), pike-like in form but with very weak
teeth, is found in tropical America. _Elops machnata_, the jack
mariddle, the awaawa of the Hawaiians, abounding in the Pacific, is
scarcely if at all different.
[Illustration:
FIG. 30.—Tarpon or Grande Écaille, _Tarpon atlanticus_ Cuv. & Val.
Florida.
]
The tarpon, called also grande écaille, silver-king, and sable (_Tarpon
atlanticus_), is a favorite game-fish along the coasts of Florida and
Carolina. It takes the hook with great spirit, and as it reaches a
length of six feet or more it affords much excitement to the successful
angler. The very large scales are much used in ornamental work.
A similar species of smaller size, also with the last ray of the dorsal
very much produced, is _Megalops cyprinoides_ of the East Indies. Other
species occur in the South Seas.
Numerous fossil genera related to _Elops_ are found in the Cretaceous
and Tertiary rocks. _Holcolepis lewesiensis_ (wrongly called
_Osmeroides_) is the best-known European species. Numerous species are
referred to _Elopopsis_. _Megalops prisca_ and species of _Elops_ also
occur in the London Eocene.
In all these the large parietals meet along the median line of the
skull. In the closely related family of _Spaniodontidæ_ the parietals
are small and do not meet. All the species of this group, united by
Woodward with the _Elopidæ_, are extinct. These fishes preceded the
_Elopidæ_ in the Cretaceous period. Leading genera are _Thrissopater_
and _Spaniodon_, the latter armed with large teeth. _Spaniodon blondeli_
is from the Cretaceous of Mount Lebanon. Many other species are found in
the European and American Cretaceous rocks, but are known from imperfect
specimens only.
_Sardinius_, an American Cretaceous fossil herring, may stand near
_Spaniodon_. _Rhacolepis buccalis_ and _Notelops brama_ are found in
Brazil, beautifully preserved in concretions of calcareous mud supposed
to be of Cretaceous age.
The extinct family of _Pachyrhizodontidæ_ is perhaps allied to the
_Elopidæ_. Numerous species of _Pachyrhizodus_ are found in the
Cretaceous of southern England and of Kansas.
=The Albulidæ.=—The _Albulidæ_, or lady-fishes, characterized by the
blunt and rounded teeth, are found in most warm seas. _Albula vulpes_ is
a brilliantly silvery fish, little valued as food. The metamorphosis
(see Fig. 112, Vol. I) which the larva undergoes is very remarkable. It
is probably, however, more or less typical of the changes which take
place with soft-rayed fishes generally, though more strongly marked in
_Albula_ and in certain eels than in most related forms. Fossils allied
to _Albula_, _Albula oweni_, _Chanoides macropomus_, are found in the
Eocene of Europe; _Syntegmodus altus_ in the Cretaceous of Kansas. In
_Chanoides_, the most primitive genus, the teeth are much fewer than in
_Albula_. _Plethodus_ and _Thryptodus_, with peculiar dental plates on
the roof and floor of the mouth, probably constitute a distinct family,
_Thryptodontidæ_. The species are found in European and American rocks,
but are known from imperfect specimens only.
[Illustration:
FIG. 31.—The Lady-fish, _Albula vulpes_ (Linnæus). Florida.
]
=The Chanidæ.=—The _Chanidæ_, or milkfishes, constitute another small
archaic type, found in the tropical Pacific. They are large, brilliantly
silvery, toothless fishes, looking like enormous dace, swift in the
water, and very abundant in the Gulf of California, Polynesia, and
India. The single living species is the _Awa_, or milkfish, _Chanos
chanos_, largely used as food in Hawaii. Species of _Prochanos_ and
_Chanos_ occur in the Cretaceous, Eocene, and Miocene. Allied to
_Chanos_ is the Cretaceous genus _Ancylostylos_ (_gibbus_), probably the
type of a distinct family, toothless and with many-rayed dorsal.
[Illustration:
FIG. 32.—Milkfish, _Chanos chanos_ (L.). Mazatlan.
]
[Illustration:
FIG. 33.—Mooneye, _Hiodon tergisus_ Le Sueur. Ecorse, Mich.
]
=The Hiodontidæ.=—The _Hiodontidæ_, or mooneyes, inhabit the rivers of
the central portion of the United States and Canada. They are shad-like
fishes with brilliantly silvery scales and very strong sharp teeth,
those on the tongue especially long. They are very handsome fishes and
take the hook with spirit, but the flesh is rather tasteless and full of
small bones, much like that of the milkfish. The commonest species is
_Hiodon tergisus_. No fossil _Hiodontidæ_ are known.
[Illustration:
FIG. 34.—_Istieus grandis_ Agassiz. Family _Pterothrissidæ_. (After
Zittel.)
]
[Illustration:
FIG. 35.—_Chirothrix libanicus_ Pictet & Humbert. Cretaceous of Mt.
Lebanon. (After Woodward.)
]
=The Pterothrissidæ.=—The _Pterothrissidæ_ are sea-fishes like _Albula_,
but more slender and with a long dorsal fin. They live in deep or cold
waters along the coasts of Japan, where they are known as gisu. The
single species is _Pterothrissus gissu_. The fossil genus _Istieus_,
from the Upper Cretaceous, probably belongs near the _Pterothrissidæ_.
_Istieus grandis_ is the best-known species. Another ancient family, now
represented by a single species, is that of the _Chirocentridæ_, of
which the living type is _Chirocentrus dorab_, a long, slender, much
compressed herring-like fish, with a saw-edge on the belly, found in the
East Indies, in which region _Chirocentrus polyodon_ occurs as a fossil.
Numerous fossil genera related to _Chirocentrus_ are enumerated by
Woodward, most of them to be referred to the related family of
_Ichthyodectidæ_ (_Saurodontidæ_). Of these, _Portheus_,
_Ichthyodectes_, _Saurocephalus_ (_Saurodon_), and _Gillicus_ are
represented by numerous species, some of them fishes of immense size and
great voracity. _Portheus molossus_, found in the Cretaceous of
Nebraska, is remarkable for its very strong teeth. Species of other
genera are represented by numerous species in the Cretaceous of both the
Rocky Mountain region and of Europe.
[Illustration:
FIG. 36.—Gigantic skeleton of _Portheus molossus_ Cope. (Photograph by
Charles H. Sternberg.)
]
=The Ctenothrissidæ.=—A related family, _Ctenothrissidæ_, is represented
solely by extinct Cretaceous species. In this group the body is robust
with large scales, ctenoid in _Ctenothrissa_, cycloid in _Aulolepis_.
The fins are large, the belly not serrated, and the teeth feeble.
_Ctenothrissa vexillifera_ is from Mount Lebanon. Other species occur in
the European chalk. In the small family of _Phractolæmidæ_ the
interopercle, according to Boulenger, is enormously developed.
[Illustration:
FIG. 37.—_Ctenothrissa vexillifera_ Pictet, restored. Mt. Lebanon
Cretaceous. (After Woodward.)
]
=The Notopteridæ.=—The _Notopteridæ_ is another small family in the
rivers of Africa and the East Indies. The body ends in a long and
tapering fin, and, as usual in fishes which swim by body undulations,
the ventral fins are lost. The belly is doubly serrate. The air-bladder
is highly complex in structure, being divided into several compartments
and terminating in two horns anteriorly and posteriorly, the anterior
horns being in direct communication with the auditory organ. A fossil
_Notopterus_, _N. primævus_, is found in the same region.
=The Clupeidæ.=—The great herring family, or _Clupeidæ_, comprises
fishes with oblong or herring-shaped body, cycloid scales, and feeble
dentition. From related families it is separated by the absence of
lateral line and the division of the maxillary into three pieces. In
most of the genera the belly ends in a serrated edge, though in the true
herring this is not very evident, and in some the belly has a blunt
edge. Some of the species live in rivers, some ascend from the sea for
the purpose of spawning. The majority are confined to the ocean. Among
all the genera, the one most abundant in individuals is that of
_Clupea_, the herring. Throughout the North Atlantic are immense schools
of _Clupea harengus_. In the North Pacific on both shores another
herring, _Clupea pallasi_, is equally abundant, and with the same market
it would be equally valuable. As salted, dried, or smoked fish the
herring is found throughout the civilized world, and its spawning and
feeding-grounds have determined the location of cities.
[Illustration:
FIG. 38.—Herring, _Clupea harengus_ L. New York.
]
The genus _Clupea_, of northern distribution, has the vertebræ in
increased number (56), and there are weak teeth on the vomer. Several
other genera are very closely related, but ranging farther south they
have, with other characters, fewer (46 to 50) vertebræ. The alewife, or
branch-herring (_Pomolobus pseudoharengus_), ascends the rivers to spawn
and has become landlocked in the lakes of New York. The skipjack of the
Gulf of Mexico, _Pomolobus chrysochloris_, becomes very fat in the sea.
The species becomes landlocked in the Ohio River, where it thrives as to
numbers, but remains lean and almost useless as food. The glut-herring,
_Pomolobus æstivalis_, and the sprat, _Pomolobus sprattus_, of Europe
are related forms.
[Illustration:
FIG. 39.—Alewife, _Pomolobus pseudoharengus_ (Wilson). Potomac River.
]
Very near also to the herring is the shad (_Alosa sapidissima_) of the
eastern coasts of America, and its inferior relatives, the shad of the
Gulf of Mexico (_Alosa alabamæ_), the Ohio River shad (_Alosa
ohiensis_), very lately discovered, the Allice shad (_Alosa alosa_) of
Europe, and the Thwaite shad (_Alosa finta_). In the genus _Alosa_ the
cheek region is very deep, giving the head a form different from that
seen in the herring.
The American shad is the best food-fish in the family, peculiarly
delicate in flavor when broiled, but, to a greater degree than occurs in
any other good food-fish, its flesh is crowded with small bones. The
shad has been successfully introduced into the waters of California,
where it abounds from Puget Sound to Point Concepcion, ascending the
rivers to spawn in May as in its native region, the Atlantic coast.
The genus _Sardinella_ includes species of rich flesh and feeble
skeleton, excellent when broiled, when they may be eaten bones and all.
This condition favors their preservation in oil as "sardines." All the
species are alike excellent for this purpose. The sardine of Europe is
the _Sardinella pilchardus_, known in England as the pilchard. The
"Sardina de España" of Cuba is _Sardinella pseudohispanica_, the sardine
of California, _Sardinella cærulea_. _Sardinella sagax_ abounds in
Chile, and _Sardinella melanosticta_ is the valued sardine of Japan.
In the tropical Pacific occur other valued species, largely belonging to
the genus _Kowala_. The genus _Harengula_ contains small species with
very large, firm scales which do not fall when touched, as is generally
the case with the sardines. Most common of these is _Harengula sardina_
of the West Indies. Similar species occur in southern Europe and in
Japan.
[Illustration:
FIG. 40.—Menhaden, _Brevoortia tyrannus_ (Latrobe). Wood's Hole, Mass.
]
In _Opisthonema_, the thread-herring, the last dorsal ray is much
produced, as in the gizzard-shad and the tarpon. The two species known
are abundant, but of little commercial importance. Of greater value are
the menhaden, or the moss-bunker, _Brevoortia tyrannus_, inhabiting the
sandy coasts from New England southward. It is a coarse and bony fish,
rarely eaten when adult, although the young in oil makes acceptable
sardines. It is used chiefly for oil, the annual yield exceeding in
value that of whale-oil. The refuse is used as manure, a purpose for
which the fishes are often taken without preparation, being carried
directly to the cornfields. From its abundance this species of inferior
flesh exceeds in commercial value almost all other American fishes
excepting the cod, the herring, and the quinnat salmon.
One of the most complete of fish biographies is that of Dr. G. Brown
Goode on the "Natural and Economic History of Menhaden."
Numerous other herring-like forms, usually with compressed bodies, dry
and bony flesh, and serrated bellies, abound in the tropics and are
largely salted and dried by the Chinese. Among these are _Ilisha
elongata_ of the Chinese coast. Related forms occur in Mexico and
Brazil.
The round herrings, small herrings which have no serrations on the
belly, are referred by Dr. Gill to the family of _Dussumieriidæ_. These
are mostly small tropical fishes used as food or bait. One of these, the
Kobini-Iwashi of Japan (_Stolephorus japonicus_), with a very bright
silver band on the side, has considerable commercial importance. Very
small herrings of this type in the West Indies constitute the genus
_Jenkinsia_, named for Dr. Oliver P. Jenkins, the first to study
seriously the fishes of Hawaii. Other species constitute the widely
distributed genera _Etrumeus_ and _Dussumieria_. _Etrumeus sardina_ is
the round herring of the Virginia coast. _Etrumeus micropus_ is the
Etrumei-Iwashi of Japan and Hawaii.
[Illustration:
FIG. 41.—A fossil Herring, _Diplomystus humilis_ Leidy. (From a
specimen obtained at Green River, Wyo.) The scutes along the back
lost in the specimen. Family _Clupeidæ_.
]
Fossil herring are plentiful and exist in considerable variety, even
among the _Clupeidæ_ as at present restricted. _Histiothrissa_ of the
Cretaceous seems to be allied to _Dussumieria_ and _Stolephorus_.
Another genus, from the Cretaceous of Palestine, _Pseudoberyx_
(_syriacus_, etc.), having pectinated scales, should perhaps constitute
a distinct subfamily, but the general structure is like that of the
herring. More evidently herring-like is _Scombroclupea_
(_macrophthalma_). The genus _Diplomystus_, with enlarged scales along
the back, is abundantly represented in the Eocene shales of Green River,
Wyoming. Species of similar appearance, usually but wrongly referred to
the same genus, occur on the coasts of Peru, Chile, and New South Wales.
A specimen of _Diplomystus humilis_ from Green River is here figured.
Numerous herring, referred to _Clupea_, but belonging rather to
_Pomolobus_, or other non-Arctic genera, have been described from the
Eocene and later rocks.
Several American fossil herring-like fishes, of the genus _Leptosomus_,
as _Leptosomus percrassus_, are found in the Cretaceous of South Dakota.
Fossil species doubtfully referred to _Dorosoma_, but perhaps allied
rather to the thread-herring (_Opisthonema_), being herrings with a
prolonged dorsal ray, are recorded from the early Tertiary of Europe.
Among these is _Opisthonema doljeanum_ from Austria.
[Illustration:
FIG. 42.—Hickory-shad, _Dorosoma cepedianum_ (Le Sueur). Potomac
River.
]
=The Dorosomatidæ.=—The gizzard-shad, _Dorosomatidæ_, are closely
related to the _Clupeidæ_, differing in the small contracted toothless
mouth and reduced maxillary. The species are deep-bodied, shad-like
fishes of the rivers and estuaries of eastern America and eastern Asia.
They feed on mud, and the stomach is thickened and muscular like that of
a fowl. As the stomach has the size and form of a hickory-nut, the
common American species is often called hickory-shad. The gizzard-shad
are all very poor food-fish, bony and little valued, the flesh full of
small bones. The belly is always serrated. In three of the four genera
of _Dorosomatidæ_ the last dorsal ray is much produced and whip-like.
The long and slender gill-rakers serve as strainers for the mud in which
these fishes find their vegetable and animal food. _Dorosoma
cepedianum_, the common hickory-shad or gizzard-shad, is found in
brackish river-mouths and ponds from Long Island to Texas, and
throughout the Mississippi Valley in all the large rivers. Through the
canals it has entered Lake Michigan. The Konoshiro, _Clupanodon
thrissa_, is equally common in China and Japan.
=The Engraulididæ.=—The anchovies (_Engraulididæ_) are dwarf herrings
with the snout projecting beyond the very wide mouth. They are small in
size and weak in muscle, found in all warm seas, and making a large part
of the food of the larger fish. The genus _Engraulis_ includes the
anchovy of Europe, _Engraulis encrasicholus_, with similar species in
California, Chile, Japan, and Australia. In this genus the vertebræ are
numerous, the bones feeble, and the flesh tender and oily. The species
of _Engraulis_ are preserved in oil, often with spices, or are made into
fish-paste, which is valued as a relish. The genus _Anchovia_ replaces
_Engraulis_ in the tropics. The vertebræ are fewer, the bones firm and
stiff, and the flesh generally dry. Except as food for larger fish,
these have little value, although existing in immense schools. Most of
the species have a bright silvery band along the side. The most familiar
of the very numerous species is the silver anchovy, _Anchovia browni_,
which abounds in sandy bays from Cape Cod to Brazil. Several other
genera occur farther southward, as well as in Asia, but _Engraulis_ only
is found in Europe. Fossil anchovies called _Engraulis_ are recorded
from the Tertiary of Europe.
[Illustration:
FIG. 43.—A Silver Anchovy, _Anchovia perthecata_ (Goode & Bean).
Tampa.
]
[Illustration:
FIG. 44.—_Notogoneus osculus_ Cope. Green River Eocene. Family
_Gonorhynchidæ_.
]
=Gonorhynchidæ.=—To the _Isospondyli_ belongs the small primitive family
of _Gonorhynchidæ_, elongate fishes with small mouth, feeble teeth, no
air-bladder, small scales of peculiar structure covering the head, weak
dentition, the dorsal fin small, and posterior without spines. The
mesocoracoid is present as in ordinary _Isospondyli_. _Gonorhynchus
abbreviatus_ occurs in Japan, and _Gonorhynchus gonorhynchus_ is found
in Australia and about the Cape of Good Hope. Numerous fossil species
occur. _Charitosomus lineolatus_ and other species are found in the
Cretaceous of Mount Lebanon and elsewhere. Species without teeth from
the Oligocene of Europe and America are referred to the genus
_Notogoneus_. _Notogoneus osculus_ occurs in the Eocene fresh-water
deposits at Green River, Wyoming. It bears a very strong resemblance in
form to an ordinary sucker (_Catostomus_), for which reason it was once
described by the name of _Protocatostomus_. The living _Gonorhynchidæ_
are all strictly marine.
In the small family of _Cromeriidæ_ the head and body are naked.
=The Osteoglossidæ.=—Still less closely related to the herring is the
family of _Osteoglossidæ_, huge pike-like fishes of the tropical rivers,
armed with hard bony scales formed of pieces like mosaic. The largest of
all fresh-water fishes is _Arapaima gigas_ of the Amazon region, which
reaches a length of fifteen feet and a weight of 400 pounds. It has
naturally considerable commercial importance, as have species of
_Osteoglossum_, coarse river-fishes which occur in Brazil, Egypt, and
the East Indies. _Heterotis nilotica_ is a large fish of the Nile. In
some or all of these the air-bladder is cellular or lung-like, like that
of a Ganoid.
Allied to the _Osteoglossidæ_ is _Phareodus_ (_Dapedoglossus_), a group
of large shad-like fossil fishes, with large scales of peculiar mosaic
texture and with a bony casque on the head, found in fresh-water
deposits of the Green River Eocene. In the perfect specimens of
_Phareodus_ (or _Dapedoglossus_) _testis_ the first ray of the pectoral
is much enlarged and serrated on its inner edge, a character which may
separate these fishes as a family from the true _Osteoglossidæ_. It does
not, however, appear in Cope's figures, none of his specimens having the
pectorals perfect. In these fishes the teeth are very strong and sharp,
the scales are very large and thin, looking like the scales of a
parrot-fish, the long dorsal is opposite to the anal and similar to it,
and the caudal is truncate. The end of the vertebral column is turned
upward.
Other species are _Phareodus acutus_, known from the jaws; _P.
encaustus_ is known from a mass of thick scales with reticulate or
mosaic-like surface, much as in _Osteoglossum_, and _P. æquipennis_ from
a small example, perhaps immature. _Phareodus testis_ is frequently
found well preserved in the shales at Fossil Station, to the
northwestward of Green River. Whether all these species possess the
peculiar structure of the scales, and whether all belong to one genus,
is uncertain.
[Illustration:
FIG. 45.—_Phareodus testis_ (Cope). From a specimen 20 inches long
collected at Fossil, Wyo., in the Museum of the Univ. of Wyoming.
(Photograph by Prof. Wilbur C. Knight.)
]
In Eocene shales of England occurs _Brychætus muelleri_, a species
closely related to _Phareodus_, but the scales smaller and without the
characteristic reticulate or mosaic structure seen in _Phareodus
encaustus_.
[Illustration:
FIG. 46.—Deposits of Green River Shales, bearing _Phareodus_, at
Fossil, Wyoming. (Photograph by Wilbur C. Knight.)
]
[Illustration:
FIG. 47.—A day's catch of Fossil fishes, _Phareodus_, _Diplomystus_,
etc. Green River Eocene Shales, Fossil, Wyoming. (Photograph by
Prof. Wilbur C. Knight.)
]
=The Pantodontidæ.=—The bony casque of _Osteoglossum_ is found again in
the _Pantodontidæ_, consisting of one species, _Pantodon buchholzi_, a
small fish of the brooks of West Africa. As in the _Osteoglossidæ_ and
in the _Siluridæ_, the subopercle is wanting in _Pantodon_.
[Illustration:
FIG. 48.—_Alepocephalus agassizii_ Goode & Bean. Gulf Stream.
]
The _Alepocephalidæ_ are deep-sea herring-like fishes very soft in
texture and black in color, taken in the oceanic abysses. Some species
may be found in almost all seas below the depth of half a mile.
_Alepocephalus rostratus_ of the Mediterranean has been long known, but
most of the other genera, _Talismania_, _Mitchillina_, _Conocara_, etc.,
are of very recent discovery, having been brought to the surface by the
deep-sea dredging of the _Challenger_, the _Albatross_, the _Blake_, the
_Travailleur_, the _Talisman_, the _Investigator_, the _Hirondelle_, and
the _Violante_.