THE MESOZOIC AGES. 217 



like those of Ichthyosaurus. Cope, who has described 

 these great creatures as they occur in the Cretaceous 

 of the United States, thus sketches the Mosasaur : * It 

 was a long and slender reptile, with a pair of powerful 

 paddles in front, a moderately long neck, and flat 

 pointed head. The very long tail was flat and deep, 

 like that of a great eel, forming a powerful pro- 

 peller. The arches of the vertebral column were more 

 extensively interlocked than in any other reptiles 

 except the snakes. In the related genus Clidastes 

 this structure is as fully developed as in the serpents, 

 so that we can picture to ourselves its well-known con- 

 sequences j their rapid progress through the water by 

 lateral undulations, their lithe motions on the land, the 

 rapid stroke, the ready coil, or the elevation of the head 

 and vertebral column, literally a living pillar, towering 

 above the waves or the thickets of the shore swamps." 

 As in serpents, the mouth was wide in its gape, 

 and the lower jaw capable of a certain separation from 

 the skull to admit of swallowing large prey. Besides 

 this the lower jaw had an additional peculiarity, seen 

 in some snakes, namely, a joint in the middle of the 

 jaw enabling its sides to expand, so that the food 

 might be swallowed " between the branches of the 

 jaw/' Perhaps no creatures more fully realize in 

 their enormous length and terrible powers the great 

 Tanninim (the stretched-out or extended reptiles) of 

 the fifth day of the Mosaic record, than the Mosa- 

 saurus and Elasmosaurus. When Mr. Cope showed 

 me, a few years ago, a nearly complete skeletoo 



