ROOM IV. RETROSPECTIVE SUMMARY. 387 



It existed in seas peopled with extinct species and genera 

 of fishes, and teeming with mollusks allied to the cuttle-fish 

 and the nautilus, but of types that perished at the close of 

 the cretaceous period. Groves of corals and of other zoo- 

 phytes, related to forms now of excessive rarity, even in 

 tropical seas, clothed the bottom of the deep ; and echino- 

 derms, star-fishes, crustaceans, and other tribes of inverte- 

 brata, were included in that prodigious assemblage of extra- 

 ordinary forms of being, which constituted the population of 

 the liassic ocean. Shoals of turtles inhabited those waters, 

 and many kinds of crocodilian reptiles frequented their shores. 



Such was the marine fauna in which the Ichthyosauri and 

 Plesiosauri held the highest place ; such the inhabitants of that 

 ocean whose waters surrounded the islands, and washed the 

 shores of the continent, that were tenanted by the stupendous 

 terrestrial herbivorous and carnivorous lizards, whose fossil 

 relics formed the subject of our previous investigations : and 

 amidst those multitudes of reptilian forms, that traversed the 

 air, or crawled on the earth, or sported in the seas, two 

 diminutive genera of quadrupeds were the sole representa- 

 tives of the Mammalia, either on the land or in the waters. 



