. Text book of vertebrate zoology. Vertebrates; Anatomy, Comparative. 2S2 CLASSIFICATION OF VERTEBRATES. the alligator gar, L. tristcechus of the southern states, reaches a length of ten feet. Allied fossil forms are numerous. Catopterus being represented in the triassic rocks of the Connecticut valley. Lepidotus ranges from the trias to the Jura of Europe. Aspidorhynchus had a snout something like that of the sword-fish. In the « (Halecomorphi) the vertebrae are amphicoelous, the scales cycloid, teeth on pterygoids as well as on vomers and palatines, no pyloric caeca. Amia calva. the b
. Text book of vertebrate zoology. Vertebrates; Anatomy, Comparative. 2S2 CLASSIFICATION OF VERTEBRATES. the alligator gar, L. tristcechus of the southern states, reaches a length of ten feet. Allied fossil forms are numerous. Catopterus being represented in the triassic rocks of the Connecticut valley. Lepidotus ranges from the trias to the Jura of Europe. Aspidorhynchus had a snout something like that of the sword-fish. In the « (Halecomorphi) the vertebrae are amphicoelous, the scales cycloid, teeth on pterygoids as well as on vomers and palatines, no pyloric caeca. Amia calva. the bow fin of the eastern U. is the only living species. The genus dates from the eocene. Allied fossil forms are Eiirycormiis, Callopterus, Caturus, and Pachycor- Tnus, ranging from the lias to the Jurassic. Legion II. Teleostei. Fishes with the bony skeleton well developed, the cranium and the vertebral centra ossified, the latter amphicoelous; tail diphy- or homocercal; spiral valve and conus arteriosus not developed; no optic chiasma; scales, when present, cvcloid or ctenoid. The group of teleosts or bony fishes so closely follows the ganoids that some students do not distinguish between them. There are, however, some dis- tinctions between the two groups, while the matter of convenience warrants their recognition. In a few teleosts the skin is naked or covered with bony plates, but usually the body is covered with scales of the cycloid or ctenoid tvpe. In a few the tail is diphycercal, but usually it is hom- ocercal. The fulcra, so characteristic of most ganoids, never occur. The skele- ton is well ossified, this being especial]\- true of the skull, where the cartilages are almost entirely replaced bv bone. The operculum and its skeleton are well developed, branchiostegals are pres- ent, and gular plates rarely occur. The paired fins never have a basal lobe ; and the ventrals, when pres- ent, may either be near the vent or far forward, beneath the. Fig. 254. Breathing val
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