156 PICTURESQUE SKETCHES 



sea, obtaining there only the means of subsist- 

 ence. 



Such a group as this existed at the time of the 

 deposit of the lias, and is there represented by two 

 genera perfectly distinct from one another, each ex- 

 hibiting several well-marked species, and both pre- 

 sent in most extraordinary abundance. The per- 

 fect skeletons of various species belonging to each 

 genus have been occasionally found embedded in 

 the rock, and other specimens have been obtained 

 in all degrees of preservation ; so that it is clear 

 that the animals must have lived long and multiplied 

 greatly in the seas which covered a great part of 

 what is now land in the northern hemisphere, shortly 

 after the completion of the deposit of the new red 

 sandstone. 



The most essential character in these animals, is 

 that they were exclusively marine in their habits ; 

 not merely taking refuge in the water occasionally, 

 like most of the crocodiles, or seeking their prey 

 there, and then, when gorged, coming ashore to sleep 

 in the marshes and jungle ; but adapted in all re- 

 spects to make use of the sea as their permanent 

 habitation, and only resorting to land from time to 

 time, probably to deposit their eggs, which would after- 

 wards be hatched by the sun.* They formed a dis- 

 tinct group, having the same relation to other reptiles 

 that the animals of the whale tribe bear to other 

 mammals ; exhibiting in all essential points the struc- 

 ture of their order, but yet having this structure so 



* It is not indeed certain that these animals were oviparous, but this 

 must be considered the most probable conclusion, at least without better 

 evidence to the contrary than has yet been presented. 



