Classification of Ganoids.—The subdivision of the series of Ganoidei into orders offers great difficulty from the fact of the varying relationships of the members of the group and the fact that the great majority of the species are known only from broken skeletons preserved in the rocks. It is apparently easy to separate those with cartilaginous skeletons from those with these bones more or less ossified. It is also easy to separate those with bony scales or plates from those having the scales cycloid. But the one type of skeleton grades into the other, and there is a bony basis even to the thinnest of scales found in this group. Among the multitude of names and divisions proposed we may recognize six orders, for which the names Lysopteri, Chondrostei, Selachostomi, Pycnodonti, Lepidostei, and Halecomorphi are not inappropriate. Each of these seems to represent a distinct offshoot from the first primitive group.

Order Lysopteri.—In the most primitive order, called Lysopteri (λυσός, loose; πτερόν, fin) by Cope, Heterocerci by Zittel and Eastman, and the "ascending series of Chondrostei" by Woodward, we find the nearest approach to the Chondropterygians. In this order the arches of the vertebræ are more or less ossified, the body is more or less short and deep, covered with bony dermal plates. The opercular apparatus is well developed, with numerous branchiostegals. Infraclavicles are present, and the fins provided with fulcra. Dorsal and anal fins are present, with rays more numerous than their supports; ventral fin with basal supports which are imperfectly ossified; caudal fin mostly heterocercal, the scales mostly rhombic in form. All the members of this group are now extinct.

The Palæoniscidæ.—The numerous genera of this order are referred to three families, the Palæoniscidæ, Platysomidæ, and Dictyopygidæ; a fourth family, Dorypteridæ, of uncertain relations, being also tentatively recognized. The family of Palæoniscidæ is the most primitive, ranging from the Devonian to the Lias, and some of them seem to have entered fresh waters in the time of the coal-measures. These fishes have the body elongate and provided with one short dorsal fin. The tail is heterocercal and the body covered with rhombic plates. Fulcra or rudimentary spine-like scales are developed on the upper edge of the caudal fin in most recent Ganoids, and often the back has a median row of undeveloped scales. A multitude of species and genera are recorded. A typical form is the genus Palæoniscum,^[5] with many species represented in the rocks of various parts of the world. The longest known species is Palæoniscum frieslebenense from the Permian of Germany and England. Palæoniscum magnum, sixteen inches long, occurs in the Permian of Germany. From Canobius, the most primitive genus, to Coccolepis, the most modern, is a continuous series, the suspensorium of the lower jaw becoming more oblique, the basal bones of the dorsal fewer, the dorsal extending farther forward, and the scales more completely imbricate. Other prominent genera are Amblypterus, Eurylepis, Cheirolepis, Rhadinichthys, Pygopterus, Elonichthys, Ærolepis, Gyrolepis, Myriolepis, Oxygnathus, Centrolepis, and Holurus.

The Platysomidæ.—The Platysomidæ are different in form, the body being deep and compressed, often diamond-shaped, with very long dorsal and anal fins. In other respects they are very similar to the Palæoniscidæ, the osteology being the same. The Palæoniscidæ were rapacious fishes with sharp teeth, the Platysomidæ less active, and, from the blunter teeth, probably feeding on small animals, as crabs and snails.

The rhombic enameled scales are highly specialized and held together as a coat of mail by peg-and-socket joints. The most extreme form is Platysomus, with the body very deep. Platysomus gibbosus and other species occur in the Permian rocks of Germany. Cheirodus is similar to Platysomus, but without ventral fins. Eurynotus, the most primitive genus, is remarkable for its large pectoral fins. Eurynotus crenatus occurs in the Subcarboniferous of Scotland. Other genera are Mesolepis, Globulodus, Wardichthys, and Cheirodopsis.

Some of the Platysomidæ have the interneural spines projecting through the skin before the dorsal fin. This condition is found also in certain bony fishes allied to the Carangidæ.

The Dorypteridæ.—Dorypterus hoffmani, the type of the singular Palæozoic family of Dorypteridæ, with thoracic or sub-jugular many-rayed ventrals, is Stromateus-like to all appearance, with distinct resemblances to certain Scombroid forms, but with a heterocercal tail like a ganoid, imperfectly ossified back-bone, and other very archaic characters. The body is apparently scaleless, unlike the true Platysomidæ, in which the scales are highly developed. A second species, Dorypterus althausi, also from the German copper shales, has been described. This species has lower fins than Dorypterus hoffmani, but may be the adult of the same type. Dorypterus is regarded by Woodward as a specialized offshoot from the Platysomidæ. The many-rayed ventrals and the general form of the body and fins suggest affinity with the Lampridæ.

Dictyopygidæ.—In the Dictyopygidæ (Catopteridæ), the body is gracefully elongate, less compressed, the heterocercal tail is short and abruptly turned upwards, the teeth are sharp and usually hooked, and the bony plates well developed. Of this group two genera are recognized, each containing numerous species. In Redfieldius (= Catopterus Redfield, not of Agassiz) the dorsal is inserted behind the anal, while in Dictyopyge this is not the case. Redfieldius gracilis and other species are found in the Triassic of the Connecticut River. Dictyopyge macrura is found in the same region, and Dictyopyge catoptera and other species in Europe.

Order Chondrostei.—The order Chondrostei (χόνδρος, cartilage; ὀστέον, bone), as accepted by Woodward, is characterized by the persistence of the notochord in greater or less degree, the endoskeleton remaining cartilaginous. In all, the axonosts and baseosts of the median fins are arranged in simple regular series and the rays are more numerous than the supporting elements. The shoulder-girdle has a pair of infraclavicular plates. The pelvic fins have well-developed baseosts. The branchiostegals are few or wanting. In the living forms, and probably in all others, a matter which can never be ascertained, the optic nerves are not decussating, but form an optic chiasma, and the intestine is provided with a spiral valve. In all the species there is one dorsal and one anal fin, separate from the caudal. The teeth are small or wanting, the body naked or covered with bony plates; the caudal fin is usually heterocercal, and on the tail are rhombic plates. To this order, as thus defined, about half of the extinct Ganoids belong, as well as the modern degenerate forms known as sturgeons and perhaps the paddle-fishes, which are apparently derived from fishes with rhombic enameled scales. The species extend from the Upper Carboniferous to the present time, being most numerous in the Triassic.

At this point in Woodward's system diverges a descending series, characterized as a whole by imperfect squamation and elongate form, this leading through the synthetic type of Chondrosteidæ to the modern sturgeon and paddle-fish, which are regarded as degenerate types.

The family of Saurorhynchidæ contains pike-like forms, with long jaws, and long conical teeth set wide apart. The tail is not heterocercal, but short-diphycercal; the bones of the head are covered with enamel, and those of the roof of the skull form a continuous shield. The opercular apparatus is much reduced, and there are no branchiostegals. The fins are all small, without fulcra, and the skin has isolated longitudinal series of bony scutes, but is not covered with continuous scales. The principal genus is Saurorhynchus (= Belonorhynchus; the former being the earlier name) from the Triassic. Saurorhynchus acutus from the English Triassic is the best known species.

The family of Chondrosteidæ includes the Triassic precursors of the sturgeons. The general form is that of the sturgeon, but the body is scaleless except on the upper caudal lobe, and there are no plates on the median line of the skull. The opercle and subopercle are present, the jaws are toothless, and there are a few well-developed caudal rays. The caudal has large fulcra. The single well-known species of this group, Chondrosteus acipenseroides, is found in the Triassic rocks of England and reaches a length of about three feet. It much resembles a modern sturgeon, though differing in several technical respects. Chondrosteus pachyurus is based on the tail of a species of much larger size and Gyrosteus mirabilis, also of the English Triassic, is known from fragments of fishes which must have been 18 to 20 feet in length.

The sturgeons constitute the recent family of Acipenseridæ, characterized by the prolonged snout and toothless jaws and the presence of four barbels below the snout. In the Acipenseridæ there are no branchiostegals and a median series of plates is present on the head. The body is armed with five rows of large bony bucklers,—each often with a hooked spine, sharpest in the young. Besides these, rhombic plates are developed on the tail, besides large fulcra. The sturgeons are the youngest of the Ganoids, not occurring before the Lower Eocene, one species, Acipenser toliapicus occurring in the London clay. About thirty living species of sturgeon are known, referred to three genera: Acipenser, found throughout the Northern Hemisphere, Scaphirhynchus, in the Mississippi Valley, and Kessleria (later called Pseudoscaphirhynchus), in Central Asia alone. Most of the species belong to the genus Acipenser, which abounds in all the rivers and seas in which salmon are found. Some of the smaller species spend their lives in the rivers, ascending smaller streams to spawn. Other sturgeons are marine, ascending fresh waters only for a moderate distance in the spawning season. They range in length from 2½ to 30 feet.

All are used as food, although the flesh is rather coarse and beefy. From their large size and abundance they possess great economic value. The eggs of some species are prepared as caviar.

The sturgeons are sluggish, clumsy, bottom-feeding fish. The mouth, underneath the long snout, is very protractile, sucker-like, and without teeth. Before it on the under side of the snout are four long feelers. Ordinarily the sturgeon feeds on mud and snails with other small creatures, but I have seen large numbers of Eulachon (Thaleichthys) in the stomach of the Columbia River sturgeon (Acipenser transmontanus). This fish and the Eulachon run in the Columbia at the same time, and the sucker-mouth of a large sturgeon will draw into it numbers of small fishes who may be unsuspiciously engaged in depositing their spawn. In the spawning season in June these clumsy fishes will often leap wholly out of the water in their play. The sturgeons have a rough skin besides five series of bony plates which change much with age and which in very old examples are sometimes lost or absorbed in the skin. The common sturgeon of the Atlantic on both shores is Acipenser sturio. Acipenser huso and numerous other species are found in Russia and Siberia. The great sturgeon of the Columbia is Acipenser transmontanus, and the great sturgeon of Japan Acipenser kikuchii. Smaller species are found farther south, as in the Mediterranean and along the Carolina coast. Other small species abound in rivers and lakes. Acipenser rubicundus is found throughout the Great Lake region and the Mississippi Valley, never entering the sea. It is four to six feet long, and at Sandusky, Ohio, in one season 14,000 sturgeons were taken in the pound nets. A similar species, Acipenser mikadoi, is abundant and valuable in the streams of northern Japan.

In the genus Acipenser the snout is sharp and conical, and the shark-like spiracle is still retained.

The shovel-nosed sturgeon (Scaphirhynchus platyrhynchus) has lost the spiracles, the tail is more slender, its surface wholly bony, and the snout is broad and shaped like a shovel. The single species of Scaphirhynchus abounds in the Mississippi Valley, a fish more interesting to the naturalist than to the fisherman. It is the smallest of our sturgeons, often taken in the nets in large numbers.

In Scaphirhynchus the tail is covered by a continuous coat of mail. In Kessleria^[6] fedtschenkoi, rossikowi, and other Asiatic species the tail is not mailed.

Order Selachostomi: the Paddle-fishes.—Another type of Ganoids, allied to the sturgeons, perhaps still further degenerate, is that of the paddle-fishes, called by Cope Selachostomi (σέλαχος, shark; στόμα, mouth). This group consists of a single family, Polyodontidæ, having apparently little in common with the other Ganoids, and in appearance still more suggestive of the sharks. The common name of paddle-fishes is derived from the long flat blade in which the snout terminates. This extends far beyond the mouth, is more or less sensitive, and is used to stir up the mud in which are found the minute organisms on which the fish feeds. Under the paddle are four very minute barbels corresponding to those of the sturgeons. The vernacular names of spoonbill, duckbill cat, and shovel-fish are also derived from the form of the snout. The skin is nearly smooth, the tail is heterocercal, the teeth are very small, and a long fleshy flap covers the gill-opening. The very long and slender gill-rakers serve to strain the food (worms, leeches, water-beetles, crustaceans, and algæ) from the muddy waters from which they are taken. The most important part of this diet consists of Entomostracans. The single American species, Polyodon spathula, abounds through the Mississippi Valley in all the larger streams. It reaches a length of three or four feet. It is often taken in the nets, but the coarse tough flesh, like that of our inferior catfish, is not much esteemed. In the great rivers of China, the Yangtse and the Hoang Ho, is a second species, Psephurus gladius, with narrower snout, fewer gill-rakers, and much coarser fulcra on the tail. The habits, so far as known, are much the same.

Crossopholis magnicaudatus of the Green River Eocene shales is a primitive member of the Polyodontidæ. Its rostral blade is shorter than that of Polyodon, and the body is covered with small thin scales, each in the form of a small grooved disk with several posterior denticulations, arranged in oblique series but not in contact. The scales are quadrate in form, and more widely separated anteriorly than posteriorly. As in Polyodon, the teeth are minute and there are no branchiostegals. The squamation of this fish shows that Polyodon as well as Acipenser may have sprung from a type having rhombic scales. The tail of a Cretaceous fish, Pholidurus disjectus from the Cretaceous of Europe, has been referred with doubt to this family of Polyodontidæ.

Order Pycnodonti.—In the extinct order Pycnodonti, as recognized by Dr. O. P. Hay, the notochord is persistent and without ossification, the body is very deep, the teeth are always blunt, the opercular apparatus is reduced, the dorsal fin many-rayed, and the fins without fulcra. The scales are rhombic, but are sometimes wanting, at least on the tail. Many genera and species of Pycnodontidæ are described, mostly from Triassic and Jurassic rocks of Europe. Leading European genera are Pycnodus, Typodus (Mesodon), Gyrodus, and Palæobalistum. The numerous American species belong to Typodus, Cœlodus, Pycnodus, Hadrodus, and Uranoplosus. These forms have no affinity with Balistes, although there is some resemblance in appearance, which has suggested the name of Palæobalistum.

Woodward places these fishes with the Semionotidæ and Halecomorphi in his suborder of Protospondyli. It seems preferable, however, to consider them as forming a distinct order.

Order Lepidostei.—We may place, following Eastman's edition of Zittel, the allies and predecessors of the garpike in a single order, for which Huxley's name Lepidostei may well be used. In this group the notochord is persistent, and the vertebræ are in various degrees of ossification and of different forms. The opercles are usually complete, the branchiostegals present, and there is often a gular plate. There is no infraclavicle and the jaws have sharp teeth. The fins have fulcra, and the supports of the fins agree in number with the rays. The tail is more or less heterocercal. The scales are rhombic, arranged in oblique series, which are often united above and below with peg-and-socket articulations. This group contains among recent fishes only the garpikes (Lepisosteus). They are closely allied to the Palæoniscidæ, but the skeleton is more highly ossified. On the other hand they approach very closely to the ancestors of the bowfin, Amia. One genus, Acentrophorus, appears in the Permian; the others are scattered through Mesozoic and Tertiary rocks, the isolated group of gars still persisting. In the gars the vertebræ are concavo-convex, with ball-and-socket joints. In the others the vertebræ are incomplete or else double-concave, as in fishes generally.

For the group here called Lepidostei numerous other names have been used corresponding wholly or in part. Rhomboganoidea of Gill covers nearly the same groups; Holostei of Müller and Hyoganoidea of Gill include the Halecomorphi also; Ginglymodi of Cope includes the garpikes only, while Ætheospondyli of Woodward includes the Aspidorhynchidæ and the garpikes.

The Semionotidæ (Stylodontidæ) are robust-bodied Ganoids, having the vertebræ developed as rings, the jaws with several rows of teeth, those of the outer row styliform.

Semionotus bergeri is a well-known species, with the body moderately elongate. Semionotus agassizi and many other species occur in the Triassic of the Connecticut valley and in New Jersey. The body is very deep in the related genus Dapedium, and the head is covered with strong bony plates. Dapedium politum is a well-known species of the English Triassic. Tetragonolepis (Pleurolepis) is a similar form, very deep and compressed, with strong, firm scales.

In the extinct family of Lepidotidæ the teeth are conical or chisel-shaped, while blunt or molar teeth are on the inside of the mouth, which is small, and the suspensorium of the mandible is vertical or inclined forward. The body is robust-fusiform, covered with rhomboid scales; the vertebræ form rings about the notochord; the teeth are either sharp or blunt. The dorsal fin is short, with large fulcra.

The best known of the numerous genera are Lepidotes, rather elongate in body, with large, blunt teeth. Of the many species of Lepidotes, Lepidotes elvensis abounds in the English and German Triassic, and Lepidotes minor in the English Triassic. Another well-known European species is Lepidotes mantelli.

The Isopholidæ (Eugnathidæ) differ from the families last named in the large pike-like mouth with strong teeth. The mandibular suspensorium is inclined backwards. The body is elongate, the vertebræ forming incomplete rings; the dorsal fin is short with large fulcra.

Isopholis dentosus is found with numerous other species in the British Triassic. Caturus furcatus is especially characteristic of Triassic rocks in Germany. Ptycholepis marshi occurs in the Connecticut valley.

The Macrosemiidæ are elongate fishes with long dorsal fin, the numerous species being found in the Triassic, Jurassic, and Cretaceous of Europe. Macrosemius rostratus has a very high, continuous dorsal. Macropistius arenatus is found in the Cretaceous of Texas, the only American species known. Prominent European genera are Notagogus, Ophiopsis, and Petalopteryx.

Intermediate between the allies of the gars and the modern herrings is the large extinct family of Pholidophoridæ, referred by Woodward to the Isospondyli, and by Eastman to the Lepidostei. These are small fishes, fusiform in shape, chiefly of the Triassic and Jurassic. The fins are fringed with fulcra, the scales are ganoid and rhombic, and the vertebræ reduced to rings. The mouth is large, with small teeth, and formed as in the Isospondyli. The caudal is scarcely heterocercal.

Of Pholidophorus, with scales joined by peg-and-socket joints and uniform in size, there are many species. Pholidophorus latiusculus and many others are found in the Triassic of England and the Continent. Pholidophorus americanus occurs in the Jurassic of South Dakota. Pleuropholis, with the scales on the lateral line, which runs very low, excessively deepened, is also widely distributed. I have before me a new species from the Cretaceous rocks near Los Angeles. The Archæomænidæ differ from Pholidophoridæ in having cycloid scales. In both families the vertebræ are reduced to rings about the notochord. From fishes allied to the Pholidophoridæ the earliest Isospondyli are probably descended.

In the Aspidorhynchidæ the snout is more or less produced, the mandible has a distinct presymphysial bone, the vertebræ are double-concave or ring-like, and the fins are without fulcra. This family constitutes the suborder Ætheospondyli. In form these fishes resemble Albula and other modern types, but have mailed heads and an ancient type of scales. Two genera are well known, Aspidorhynchus and Belonostomus. Aspidorhynchus acutirostris reaches a length of three feet, and is found in the Triassic lithographic stone of Bavaria. Other species occur in rocks of Germany and England.

Belonostomus has the snout scarcely produced. Belonostomus sphyrænoides is the best known of the numerous species, all of the Triassic, Jurassic, and Cretaceous.

Family Lepisosteidæ.—The family of Lepisosteidæ, constituting the suborder Ginglymodi (γιγγλυμός, hinge), is characterized especially by the form of the vertebræ.

These are opisthocœlian, convex in front and concave behind, as in reptiles, being connected by ball-and-socket joints. The tail is moderately heterocercal, less so than in the Halecomorphi, and the body is covered with very hard, diamond-shaped, enameled scales in structure similar to that of the teeth. A number of peculiar characters are shown by these fishes, some of them having often been regarded as reptilian traits. Notable features are the elongate, crocodile-like jaws, the upper the longer, and both armed with strong teeth. The mandible is without presymphysial bone. The fins are small with large fulcra, and the scales are nearly uniform in size.

All the species belong to a single family, Lepisosteidæ, which includes the modern garpikes and their immediate relatives, some of which occur in the early Tertiary. These voracious fishes are characterized by long and slender cylindrical bodies, with enameled scales and mailed heads and heterocercal tail. The teeth are sharp and unequal. The skeleton is well ossified, and the animal itself is extremely voracious. The vertebræ, reptile-like, are opisthocœlian, that is, convex in front, concave behind, forming ball-and-socket joints. In almost all other fishes they are amphicœlian or double-concave, the interspace filled with gelatinous substance. The recent species, and perhaps all the extinct species also, belong to the single genus Lepisosteus (more correctly, but also more recently, spelled Lepidosteus). Of existing forms there are not many species, three to five at the most, and they swarm in the lakes, bayous, and sluggish streams from Lake Champlain to Cuba and along the coast to Central America. The best known of the species is the long-nosed garpike, Lepisosteus osseus, which is found throughout most of the Great Lake region and the Mississippi Valley, and in which the long and slender jaws are much longer than the rest of the head. The garpike frequents quiet waters and is apparently of sleepy habit. It often lies quiet for a long time, carried around and around by the eddies. It does not readily take the hook and seldom feeds in the aquarium. It feeds on crayfishes and small fishes, to which it is exceedingly destructive, as its bad reputation indicates. Fishermen everywhere destroy it without mercy. Its flesh is rank and tough and unfit even for dogs.

In the young garpike the caudal fin appears as a second dorsal and anal, the filamentous tip of the tail passing through and beyond it.

The short-nosed garpike, Lepisosteus platystomus, is generally common throughout the Mississippi Valley. It has a short broad snout like the alligator-gar, but seldom exceeds three feet in length. In size, color, and habits it agrees closely with the common gar, differing only in the form of the snout. The form is subject to much variation, and it is possible that two or more species have been confounded.

The great alligator-gar, Lepisosteus tristœchus, reaches a length of twenty feet or more, and is a notable inhabitant of the streams about the Gulf of Mexico. Its snout is broad and relatively wide, and its teeth are very strong. It is very destructive to all sorts of food-fishes. Its flesh is worthless, and its enameled scales resist a spear or sometimes even shot. It breathes air to a certain extent by its lungs, but soon dies in foul water, not having the tenacity of life seen in Amia.

Embryology of the Garpike.—Mr. Alexander Agassiz has given an account of the embryology of the garpike, of which the following is an abstract:

"The garpike comes up the St. Lawrence in May, lays its eggs about the 20th, and then disappears. The eggs are large, viscous, stick fast in an isolated way to whatever they fall upon, and look much like those of toads, having a large outer membrane and a small yolk. Artificial fecundation failed, but about 500 naturally-laid eggs were secured, of which all but 30 perished through mold. The young began to hatch in six days. Out of 30 young hatched, 27 lived until the 15th of July. Connection with the sharks appears in the similarity of the branchial arches and by the presence of the lateral fold in which the pectoral fins are formed; the way the tail is developed is very like that of the bony fishes. Among the Ganoids it appears, as well as in ordinary fishes, the dorsal cord is straight at first, then assumes a slightly upward curve at the extremity, when finally there appears the beginning of a lobe underneath, pointing to a complete heterocercal tail. All this is as in the bony fishes, but this is the permanent condition of the garpike, while in the bony fishes the extremity of the dorsal cord becomes extinct. The mode of development of the pectoral lobe (very large in this species) furnishes another resemblance. In the brain, and in the mode of formation of the gills, a likeness to the sharks is noticeable. The young garpikes move very slowly, and seem to float quietly, save an exceedingly rapid vibration of the pectorals and the tip of the tail. They do not swim about much, but attach themselves to fixed objects by an extraordinary horseshoe-shaped ring of sucker-appendages about the mouth. These appendages remain even after the snout has become so extended that the ultimate shape is hinted at; and furthermore, it is a remnant of this feature that forms the fleshy bulb at the end of the snout in the adult. The investigations thus far show that the young garpike has many characteristics in common with the sharks and skates, but it is not so different from the bony fishes as has been supposed."

Fossil Garpikes.—A number of fossil garpikes, referred by Cope to the genus Clastes and by Eastman and Woodward to Lepidosteus, are found in the Eocene of Europe and America. The most perfect of these remains is called Lepisosteus atrox, upward of four feet long, as large as an alligator-gar, which the species much resembles. Although found in the Eocene, Dr. C. R. Eastman declares that "it has no positively archaic features. If we inquire into the more remote or pre-Eocene history of Lepidosteids, palæontology gives no answer. They blossom forth suddenly and fully differentiated at the dawn of the Tertiary, without the least clue to their ancestry, unheralded and unaccompanied by any intermediate forms, and they have remained essentially unchanged ever since."

Another fossil species is Lepisosteus fimbriatus, from the Upper Eocene of England. Scales and other fragments of garpikes are found in Germany, Belgium, and France, in Eocene and Miocene rocks. On some of these the nominal genera Naisia, Trichiurides, and Pneumatosteus are founded. Clastes, regarded by Eastman as fully identical with Lepisosteus, is said to have the "mandibular ramus without or with a reduced fissure of the dental foramen, and without the groove continuous with it in Lepisosteus. One series of large teeth, with small ones external to them on the dentary bone." Most of the fossil forms belong to Clastes, but the genus shows no difference of importance which will distinguish it from the ordinary garpike.

Order Halecomorphi.—To this order belong the allies, living or extinct, of the bowfin (Amia), having for the most part cycloid scales and vertebræ approaching those of ordinary fishes. The resemblance to the Isospondyli, or herring group, is indicated in the name (Halec, a herring; μορφή, form). The notochord is persistent, the vertebræ variously ossified. The opercles are always complete. The branchiostegals are broad and there is always a gular plate. The teeth are pointed, usually strong. There is no infraclavicle. Fulcra are present or absent. The supports of the dorsal and anal are equal in number to the rays. Tail heterocercal. Scales thin, mostly cycloid, but bony at base, not jointed with each other. Mandible complex, with well-developed splenial rising into a coronoid process, which is completed by a distinct coronoid bone. Pectoral fin with more than five actinosts; scales ganoid or cycloid. In the living forms the air-bladder is connected with the œsophagus through life; optic chiasma present; intestine with a spiral valve. This group corresponds to the Amioidei of Lütken and essentially to the Cycloganoidei of Gill. The Protospondyli (προτός, before; σπόνδυλος, vertebra) of Woodward contains essentially the same elements.

Pachycormidæ.—In the family of Pachycormidæ the notochord is persistent, the ethmoids and vomer fused and projecting between the maxillaries to form the prominent snout, the teeth large, the body fusiform, the dorsal short, with slender rays and few fulcra or none, and the scales are thin and rhombic. The numerous species are characteristic of the Triassic, Jurassic, and Cretaceous. In Sauropsis (longimana) the body is elongate, and the pectoral fins are large and sickle-shaped. Euthynotus has small fulcra. In Pachycormus (macropterus, esocinus, etc.) the form is robust and the ventral fins are wanting. In Hypsycormus ventrals are present, and the caudal deeply forked.

In the American family of Protosphyrænidæ the jaws are armed with very strong teeth, as in the Barracuda, which, however, the species do not resemble in other respects. Protosphyræna nitida, perniciosa, and numerous other extinct forms, some of them of large size, were voracious inhabitants of the Cretaceous seas, and are found fossil, especially in North Carolina and Kansas. Numerous species called Erisichthe and Pelecopterus are all referred by Hay to Protosphyræna. In this family the scapula and coracoids are ossified, and perhaps the vertebræ also, and, as Dr. Hay has recently suggested, the Protosphyrænidæ may really belong to the Isospondyli. In any event, they stand on the border-line between the most fish-like of the Ganoids and the most archaic of the bony fishes.

The Liodesmidæ (genus Liodesmus) are much like Amia, but the notochord is persistent, its sheath without ossification. Liodesmus gracilis and L. sprattiformis occur in the lithographic stones of Bavaria. Woodward places Liodesmus with Megalurus among the Amiidæ.

The Bowfins: Amiidæ.—The Amiidæ have the vertebræ more complete. The dorsal fin is many-rayed and is without distinct fulcra. The diamond-shaped enameled scales disappear, giving place to cycloid scales, which gradually become thin and membranous in structure. A median gular plate is developed between the branchiostegals. The tail is moderately heterocercal, and the head covered with a bony coat of mail.

The family of Amiidæ contains a single recent species, Amia calva, the only living member of the order Halecomorphi. The bowfin, or grindle, is a remarkable fish abounding in the lakes and swamps of the Mississippi Valley, the Great Lake region, and southward to Virginia, where it is known by the imposing but unexplained title of John A. Grindle. In the Great Lakes it is usually called "dogfish," because even the dogs will not eat it, and "lawyer," because, according to Dr. Kirtland, "it will bite at anything and is good for nothing when caught."

The bowfin reaches a length of two and one half feet, the male being smaller than the female and marked by an ocellated black spot on the tail. Both sexes are dark mottled green in color. The flesh of the species is very watery, pasty, much of the substance evaporating when exposed to the air. It is ill-flavored, and is not often used as food. The species is very voracious and extremely tenacious of life. Its well-developed lung enables it to breathe even when out of the water, and it will live in the air longer than any other fish of American waters, longer even than the horned pout (Ameiurus) or the mud-minnow (Umbra). As a game fish the grindle is one of the very best, if the angler does not care for the flesh of what he catches, it being one of the hardest fighters that ever took the hook.

The Amiidæ retain many of the Ganoid characters, though approaching more nearly than any other of the Ganoids to the modern herring tribe. For this reason the name Halecomorphi (shad-formed) was given to this order by Professor Cope. The gular plate found in Amia and other Ganoids reappears in the herring-like family of Elopidæ, which includes the tarpon and the ten-pounder.

Woodward unites the extinct genera called Cyclurus, Notæus, Amiopsis, Protamia, Hypamia, and Pappichthys with Amia. Pappichthys (corsoni, etc.), from the Wyoming Eocene, is doubtless a valid genus, having but one row of teeth in each jaw, and Amiopsis is also recognized by Hay. Woodward refers to Amia the following extinct species: Amia valenciennesi, from the Miocene of France; Amia macrocephala, from the Miocene of Bohemia; and Amia ignota, from the Eocene of Paris. Other species of Amia are known from fragments. Several of these are from the Eocene of Wyoming and Colorado. Some of them have a much shorter dorsal fin than that of Amia calva and may be generically different.

The genus Megalurus differs from Amia in the still shorter dorsal fin, less than one-third the length of the back. The body is elongate and much depressed. Megalurus lepidotus and several other species are found in the lithographic stones of Bavaria and elsewhere.

The Oligopleuridæ.—In the extinct family Oligopleuridæ the scales are cycloid, the bones of the head scarcely enameled, and the vertebræ well ossified. Fulcra are present, and the mouth is large, with small teeth. The genera are Oligopleurus, Ionoscopus, and Spathiurus, the species not very numerous and chiefly of the Cretaceous. Ionoscopus cyprinoides of the lithographic shales of Bavaria is a characteristic species.

From the three families last named, with the Pholidophoridæ, there is an almost perfect transition from the Ganoid fishes to teleosteans of the order of Isospondyli, the primitive order from which all other bony fishes are perhaps descended. The family of Leptolepidæ, differing from Oligopleuridæ in the absence of fulcra, is here placed with the Isospondyli, but it might about as well be regarded as Ganoid.