534 HISTORICAL PALEONTOLOGY. 



From the above table it will be seen, that amongst the Gas- 

 teropoda the Trias has yielded the characteristically Palaeozoic 

 Loxonema, Holopdla, Murchisonia, and Euomphalus, all of 

 which commence their existence in the Silurian period. With 

 these are forms like Scoliostoma and Platystoma, which are 

 characteristically Triassic, and these are associated with such 

 a typical Jurassic genus as Nerincea. Amongst the Bivalves, 

 we find the Palaeozoic Megalodon side by side with the Triassic 

 Monotis and Myophoria, these being associated with the Tri- 

 gonice, Plicatulce, and Oysters of later deposits. The Brachi- 

 opods exhibit the Palaeozoic Cyrtia, with the Triassic Koninc- 

 kia, and the modern genus Thecidium. Lastly, amongst the 

 Cephalopods, this same intermingling of old and new types is 

 shown in its most striking form. The ancient genera Orthoceras, 

 Cyrtoceras, and Goniatites appear here for the last time upon 

 the scene. With these are the first Dibranchiate Cephalopods, 

 represented by the great Mesozoic genus Belemnites. The 

 Amntonitidce, with the disappearance of the comparatively 

 simple Goniatites, are represented by the more complex Cera- 

 iites, which is exclusively Triassic ; whilst the still more com- 

 plicated genus Ammonites makes its first appearance here, and 

 is never again wanting till we reach the close of the Mesozoic 

 period. 



The Vertebrata are represented in the Triassic period ap- 

 parently by members of all the existing classes. Fishes are 

 very numerous, and belong chiefly to the Hybodonts, Acro- 

 donts, and Ganoids. Amongst the more important forms we 

 find the Palaeozoic genera Palaoniscus and AmMypterus, with 

 the Secondary Hybodtis and Acrodus, and the Triassic genus 

 Saurichthys. We may also assert now with tolerable safety, 

 that the order of the Dipnoous Fishes was represented in 

 Triassic times by various species of the genus Ceratodus. 



The Amphibians of the Trias are known both by the actual 

 bones and teeth, and still more commonly by their footprints. 

 They belonged exclusively to the order of the Labyrinthodon- 

 tia, which disappears finally at the close of this period. 



Of the living orders of the Reptiles, the Chelonians are only 

 known by more or less doubtful footprints ; the Lacertilians 

 are represented by Telerpeton and Rhynchosaurus (the last often 

 referred to the Dicynodonts) ; the Crocodilia are represented 

 by Stagonolepis, Belodon, Thecodontosaurus, and Palceosaurus 

 (the last two referred by Huxley to the Deinosaurs) ; and the 

 Ophidians do not appear to have yet commenced their exist- 

 ence. Of the extinct orders of Reptiles, the Pterosaurs are 

 unknown in the Trias, and the Ichthyosaurs are not with cer- 



