MESOZOIO. 27 



American. European. 



KiMMERIDGE. 



HypsirJiophus. Omosaurus. 



Caulodon. f Caulodon.* 



Oxford. 



Epanterias. Streptospondylus. 



Oolite. 



" Cetiosaurus." 

 ? Megalosaurus. Megalosaurus. 



From the above table it will be seen how difficult it is to parallelize 

 the related beds of the Jurassic periods of the two continents at the present 

 time. All that can be said is, that many types resemblingf nearly those of 

 different horizons of the European Jurassic are found to have lived together 

 or near together in the Rocky Mountain region of North America. 



That the Cretaceous fauna of North America was the richest in the 

 cold-blooded Vertehrata is indicated by the present state of discovery. The 

 ocean of the interior of the continent deepened from the beginning of the 

 period until the epoch of the Niobrara, and then gradually shallowed until 

 the elevations of the bottom began to divide the waters. The closing 

 scenes of this great period were enacted amid a labyrinth of lagoons and 

 lakes of brackish and fresh water, whose deposits form the beds of the 

 Laramie epoch. 



The fauna of the deep-sea epoch, the Niobrara, is the best known. 

 Here the i-emains of Pythonomorpha constitute its prevailing characteristic, 

 while Elasmosaurus and Polycotylus, with but few species, represent the 

 numerous Sauropterygia of Europe. Crocodiles were apparently wanting, 

 while turtles and a peculiar group of Pterosauria were only moderately 

 abundant. The fish fauna was very rich and varied. Here the Saurodon- 

 tidcB, like the molluscous family of the Eudistes, appeared and as soon dis- 



* Iguanodon prcecursor Sauv. 



t A near affinity has been shown by Professor Owen to exist between Eucamerotus and Camarasau- 

 rut. Profegaor Owen believes these genera to be identical ; bnt the neoral spines of the anterior dorsal 

 vertebra are very different, being single in the former and doable in the latter. 



