336 



PALEOZOIC TIME. 



to the May -flies, twice the natural size, from Morris, Illinois ; and Fig- 

 670, two wings of another related species. Figure 671 represents 

 one of the posterior wings of a Cockroach, from Arkansas. Morris, 

 Illinois, and Pennsylvania, also, have afforded specimens of the Cock- 

 roach family. Other insects have been found in Nova Scotia. One, 

 called Haplophlebium by Scudder, resembles much that of Fig. 599, 

 both in the nervures of the wing, and in size ; the expanse of wing, 

 observes Dawson, was seven inches, — indicating a species of May-fly 

 much larger than any now living. May-flies are the kind of insect 

 most likely to be preserved in rock deposits, because they frequent wet 

 places. 



Passing to Vertebrates, the class of Fishes had only Selachians 

 and Ganoids, as in the Devonian ; and the Ganoids had still the an- 

 cient feature of vertebrated tails. Two of these Ganoids, one with the 



673-677. 



Ganoids. — Fig. 673, Eurjiepis tuberculatus ; 674, Coelacanthus elegans. Selachians. — Fig. 675, 

 Petalodus destructor; Fig. 676, Fin-spine ; Fig. 677 a, b, Dermal tubercles of Petrodus occi- 

 dentals. 



vertebral column extending along the middle of the tail, are illustrated 

 in Figs. 673, 674 ; they are from a black shale of the Coal-measures, 

 at Linton, Ohio, where fossil species have been found in large numbers. 

 Many teeth and fin-spines of sharks occur in the rocks. A tooth of 

 one of them, Petalodus destructor, of the tribe of Petalodonts (so 

 named from the broad leaf -like form), is shown, one third the natural 

 size, in Fig. 675 : it is from Illinois. A portion of the fin-spine of 

 another is represented in Fig. 676. At localities of this spine, there 

 are frequently bony pieces, Figs. 677 a, b, which are regarded as the 

 bony tubercles with which the surface of the body was armed. Both 

 spine and tubercles have been referred to the same species, Petrodus 

 occidentalis. 



Among Reptiles x there were both Amphibians and true Reptiles ; 

 but the former were much the most numerous. 



1 The following are the general characteristics of Eeptiles and of their subdi- 

 visions : — 



Reptiles are cold-blooded animals, like Fishes, but air-breathing, like Birds and 



