54 



VEBTEBRATA. 



dominating reptiles of tlie American Cretaceous, fifty American 

 species being enumerated by Cope, but only four from European 

 Cretaceous. 



No. 80. [263]. Mosasaurus Hoffmanni, Manteil. 



Lower Jaw, right ramus (cast). This is the most remarkable generaliza- 

 tion of the lacertilian type in the Cretaceous Period. It had large pointed 

 teeth, pyramidal and slightly recurved, expanding at the base, which was 

 anchylosed to the top of the alveolar ridge. In the lower jaw there were 

 fourteen teeth on each side, and in the upper, eleven ; and Cuvier supposed 

 that the intermaxillary bone, which was wanting, contained three more. In 

 addition to these, the gigantic reptile had its pteryoid bone armed with teeth, 

 like the Iguana. The vertebrae were concavo-convex like those of living 

 Crocodiles, Monitors and Iguanas. The length of this species has been es- 

 timated at twenty-five feet. The jaw is part of the celebrated specimen now 

 in the Garden of Plants, which was discovered in 1780 by Dr. Hoffman, in 

 the Upper Chalk, near Maestricht, Netherlands. Size, 3 ft. 1 in. x 11 in. 



No. 81. [1292] Liodon . 



Head, on slab (cast). This genus is distinguished, according to Cope, by 

 compressed teeth, lenticular in cross-section; vertebral processes not articulat- 

 ing; chevron bones free; and the humerus small and slender. The form is 

 rare in Europe, but abounds in America. L. dyspelor, Cope, and L. proriger, 

 Cope, are two of the largest species. 



The original of 

 this cast is in pos- 

 session of Ward & 

 Howell, and has 

 not been studied, 

 but probably be- 

 longs to one of the 

 two species men- 

 tioned above. 



From the Cre- 

 taceous chalk of 

 Treyo Co. , Kansas. 

 Size, 2-7 X 1-9. 



ORDER CROCODILIA. 



Here belong the higliest and largest of living reptiles. In the 

 structure of the heart, brain and stomach they approach the birds. 

 They are covered with a cuirass of square plates placed in longi- 

 tudinal lines; the jaws are united into a solid mass; the premax- 

 illary is double ; the teeth are set in sockets in a single row ; the 

 vertebrae of Cretaceous, Tertiary and living species are concavo- 

 convex ; of all others, either doubly flat, doubly concave or con- 

 vexo-concave. 



