TRIASSIC PERIOD. 411 



tion, Ostracoids ; and some of the species occurred in great numbers. 

 Three varieties of them are represented in Figs. 711, a, b. The only 

 fossil Insect observed is the larve (or exuvia of the larve) of a Neu- 

 ropter (Fig. 712) related to the genus Ephemera, from Turner's Falls, 

 on the Connecticut ; it is about three-quarters of an inch long. 



But, although relics of Insects and of Crustaceans other than Ostra- 

 coids were rare, several species of these classes of Invertebrates, and 

 also of Worms, are indicated by the tracks which they left on the fine 

 mud, that is now shale. Figs. 713-717 represent some of these foot- 



713 



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p 



it 





/ 





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*N 





i N 





o 



Figs. 713-717. 

 714 710 i 716V v 



A / 



A 



t 



vi U 



Vi v \ 



\ 



r\ / N v. [i 



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Figs. 713-715, Tracks of Insects ; 716, 717, Tracks of Crustaceans (?). 



marks. Those of Insects were probably made by larves which lived 

 in water, like those of many Neuropters. Nearly thirty species of 

 Articulates have been named by Hitchcock from the tracks. 



The Vertebrates thus far made known, by their fossils and foot- 

 prints, outnumber all other known kinds of animal life ; and many 

 were of remarkable size. They included not only Fishes and Reptiles, 

 but also the first of Mammals, and probably also the first of Birds. 

 Thus the sub-kingdom of Vertebrates had, from this earliest period of 

 the Mesozoic, all its grander subdivisions or classes represented. 



The Fishes were all Ganoids (Fig. 718). Unlike the Paleozoic, 



Fig. 718. 



Fig. 718, GANOrD, Catopterus gracilis (XX) i a i Scale of same, natural size. 



they include, along with species having vertebrated tails, others that 

 have the tails only half-vertebrated, or not vertebrated at all ; and this 



