194 GEOLOGY. 



genus were more flexible, and much more elegant inform than the 

 Liodons, and also less in size. " Perhaps to prevent their distor- 

 tions from dislocating the vertebral column, they had an additional 

 pair of articulations at each end." (Cope.) One of these species 

 Clidastes tortor, (Cope), was only thirty feet long, but its narrow 

 pointed head had a length of thirty inches. Its teeth had cutting 

 edges lengthwise of the animal, and in the lower jaw were eighteen 

 in number. " The palate was armed with eleven teeth.'" The 

 light and slender bones and elongated vertebrae indicated that this 

 reptile was of exceptionally slender proportions. The largest species 

 [Clidastes cineriaruni), was about forty feet in length. Another 

 species, remarkable for its elegance and lance-shaped head, was de- 

 scribed by Marsh, and named by him Clidastes pumilus. It was 

 only about twelve feet in length. Altogether, Marsh has described 

 from the Niobrara Cretaceous five species, Cope three, and Leidy 

 one species. 



Closely related to the preceding genus is that of Platecarpus. 

 Of the species assigned to this genus, seven were described by Cope 

 and four by Marsh. These reptiles were almost equally abundant 

 with those in the preceding genera in the old Niobrara Cretaceous 

 seas. 



Tortoises have long been known from the Cretaceous of the At- 

 lantic coast, but have only lately been described from the Niobrara 

 group. Three genera and as many species are now known. The 

 largest (Protostega gigas, Cope), had a spread of expanded flippers 

 of over fifteen feet. The ribs in this species did not entirely coal- 

 esce, and in its entire structure it was like an ordinary turtle just 

 hatched. 



European writers describe an immense number of flying reptiles 

 (Pterosaurs), from the chalk. Prof. Owen and Von Meyer first 

 made known their true structure, since which time they have ex- 

 cited much interest among geologists. All sizes, from minute 

 forms to those with an expanse of twenty-five feet of wing, have 

 been found in the European chalk. Those that I found in Ne- 

 braska were so fragile that they fell to pieces in excavating them. 

 Prof. Marsh has described one from the Niobrara of Kansas, with 

 a spread of wing of eighteen feet, and one (Pterodaetvlus ingens), 

 with a spread of twenty-three to twenty-five feet. The one that 

 Cope has described, from the same region, (P. umbrosus) r was still 

 larger, having, as he claims, a spread of twenty-five feet. Marsh 



