VERTEBRATE LIFE IN AMERICA. 5 i 5 



laid down, this class was well represented. During the remainder of 

 the Devonian, fishes continue abundant in the shallower seas, and, so 

 far as now known, were the only type of vertebrate life. These fishes 

 were mainly Ganoids, a group represented in our present waters by 

 the gar-pike (Lepidosteus) and Sturgeon (Acipenser), but, in the 

 Devonian sea, chiefly by the Placoderms, the exact affinities of which 

 are somewhat in doubt. With these were Elasmobranchs, or the 

 Shark tribe, and among them a few Chimaeroids, a peculiar type, of 

 which one or two members still survive. The Placoderms were the 

 monarchs of the ocean. All were well protected by a massive coat of 

 armor, and some of them attained huge dimensions. The American 

 Devonian fishes now known are not so numerous as those of Europe, 

 but they were larger in size, and mostly inhabitants of the open sea. 

 Some twenty genera and forty species have been described. 



The more important genera of Placoderms are Dinichthys, Aspid- 

 ichthys, and Diplognathus, our largest Palaeozoic fishes. Others are 

 Acanthaspis, Acantholepis, Coccosteus, MacropetaUchthys, and Ony- 

 chodus. Among the Elasmobranchs were Cladodus, Ctenacanthus, 

 31achoer acanthus, Rhynchodus, and Ptyctodus, the last two being 

 regarded as Chinueroids. In the Chemung epoch, the great Dipterian 

 family was introduced with Dipterus, Heliodus, and possibly Cera- 

 todus. Species of the European genera, Bothriolepis and Holopty- 

 chius, have likewise been found in our Devonian deposits. 



With the close of the Devonian, came the almost total extinction 

 of the great group of Placoderms, while the Elasmobranchs, which 

 had hitherto occupied a subordinate position, increase in numbers and 

 size, and appear to be represented by Sharks, Rays, and Chiimeras. 

 Among the members of this group from the Carboniferous, were 

 numerous Cestracionts, 1 species of Cochliodus of large size, with oth- 

 ers of the genera Deltodus, Helodus, Psammodus, and Sandalodus. 

 Of the Petalodonts there were Antliodus, Chomatodus, Ctenoptychius, 

 Petalodus, and Petalorhynchus ; and of the Hybodonts, 2 the genera 

 Cladodus, Carcharopsis, and Dlplodus. These Elasmobranchs were the 

 rulers of the Carboniferous open sea, and more than one hundred 

 species have been found in the lower part of this formation alone. 

 The Ganoids, although still abundant, were of smaller size, and deni- 

 zens of the more shallow and confined waters. The latter group of 

 fishes was represented by true Lepidostidse, of the genera Palcea- 

 niscus, Amblypterus, Platysomus, and Eurylepis. Other genera are 

 Rhizodus, Megalichthys, Ctenodus, Edestus, Orodus, Ctenacanthus, 

 Gyracanthus, and Coelacanthus. Most of these genera occur also in 

 Europe. 



From the Permian rocks of America no vertebrate remains are 



1 (Ceslracion sharp tool) a group of sharks, so named from their denticulated dor- 

 sal spines. 



2 (Hybodus = hump-tooth) a group of sharks. 



