158 GEOLOGICAL DISTEIBUTION. 



corals have been succeeded by the modern type of the star-corals, 

 Zoantharia perforata and aporosa (Montlivaltia, Thecosmilia, Isas- 

 trtea, ThamnastrsBa, &c.), whose fragmentary remains build up giant 

 reefs (Alps) ; and, similarly, the more distinctive ancient group of 

 the Echinodermata, the crinoids, whose most characteristic repre- 

 sentatives at this period are Encrinus and Pentacrinus, find their 

 successors largely in the more modern Echinoidea, or true urchins 

 (Cidaris, Hemicidaris, Hypodiadema). 



It is, however, in the vertebrate fauna that we find the most 

 prominent feature separating the life of this period from that of any 

 of the periods preceding. Not only do we meet here with the re- 

 mains of fishes, amphibians, and reptiles, but with those of mam- 

 mals, and not improbably also with the impressions or tracks of 

 birds. Granting these last, which are, however, a little uncertain, 

 it may be assumed that all the classes of the animal kingdom, as 

 now recognised by naturalists, had their representatives. The fishes 

 are still principally referable to the predominant type of the periods 

 preceding, the ganoids, which also in a measure retain the embry- 

 onic heterocercal tail, although a tendency towards homocercality is 

 observable in some of the genera, as in Semionotus. The more 

 numerously represented forms — Ischypterus, Catopterus, Semionotus 

 — belong to the group typified in the American gar-flshes, and may 

 be looked upon as the direct descendants of the Carboniferous 

 and Permian Palseonisci. The lung-fishes find an abimdant repre- 

 sentation in the teeth of Ceratodus, which, as has already been 

 seen, dates from the Permian, and possibly from a still older 

 period. This animal furnishes us with one of those rare instances 

 where a genus of living vertebrates has been founded upon the 

 fossil remains. 



The amphibians of the Triassic period show but little advance 

 over the type of their predecessors, all the forms still belong- 

 ing to the single order Labyrinthodontia, some of whose members 

 attained to prodigious dimensions (Mastodonsaurus, Labyrintho- 

 don). To this group are probably referable the singular hand- 

 shaped impressions of the animal known as Cheirotherium, or 

 "hand-beast," originally supposed to have been an animal of the 

 frog-type, but now assumed to have been a salamaudroid, or animal 

 allied to the newts, and, like them, provided with a tail, although 

 possessing in the structiu-e of the skull certain features belonging 



