TRIASSIC ERA. 125 



connecting forms in the strata of other triassic regions. When 

 we turn to the Mollusca, the record becomes much more 

 satisfactory and connective, though many of the old genera 

 are evidently on the wane, and several have wholly de- 

 parted. The brachiopods, diminishing alike in generic and 

 numerical force, are still represented by lingula, terebratula, 

 and spirifer; the conchifera, or true bivalves, are vastly on 

 the increase, and such forms as trigonia, my a, plagiostoma, 

 avicula, and ostrea, throng the waters; the gasteropods 

 present buccinum, turbo, turiteUa, and other characteristic 

 genera ; while the predaceous cephalopods, rising in com- 

 plexity of structure, are represented by orthoceras, nautilus, 

 cemtite, belemnite, and rhyncholite. The Fishes of the pe- 



Bestored form of Labyrinthodon, with footprints the same as Cheirotherium. 



riod present as yet few well-determined forms, being known 

 chiefly by their detached teeth and fin-spines. These or- 

 ganisms, scattered as they are, clearly point to shark-like 

 genera (ceratodus, hybodus, &c.), whose mouths, like that of 

 the Australian cestracion, were paved with broad-crowned 

 corrugated teeth for the crushing of shell-fish, \vhile their 

 serrated fin-spines supplied them with a sure and ready 

 means of defence. Besides these, there are other forms 

 (saurichthys, &c.) which still carry forward, though on a 



