386 GEOLOGICAL SURVEY OF THE TERRITORIES. 



flattened tail, which they used, like the eels and sea-snakes, as an oar. 

 The Sauropterygia were generally stout-bodied and with a very markedly 

 distinct neck. In the Pythonomorplia, on the other hand, the body was 

 snake-like, with narrow chest and neck scarcely differing- in diameter. 

 They were immensely elongate, and might be called sea-serpents with 

 considerable propriety. 



Of Sauropterygia, Polycotylus had a slender neck and very stout 

 limbs ; but in Elasmosaurus the neck attained dimensions exceeding that 

 of any vertebrated animal. The species E. platyurus was probably the 

 longest of the order, measuring perhaps fifty feet, but of this the neck 

 amounted to twenty-two feet. This creature was carnivorous, and could, 

 no doubt, like the snake-bird, swim at a considerable distance below the 

 surface of the water and reach to the surface for air, or explore the 

 depths or plunge for fishes to the depth of forty feet. 



Among the Pythonomorplia the Liodon dyspelor is the largest species 

 and the Clidastes intermedins the smallest. A specimen of Mosasaurus 

 missuriensis obtained by William Webb near Topeka is stated by him 

 to measure seventy-five feet in length. Should this be substantiated, 

 the L. dyspelor was at least one-third larger. This is, however, as yet 

 uncertain. 



The upper arm bones of the Clidastes are remarkably short and wide, 

 and furnished with strong processes for the insertion of muscles. They 

 are among reptiles much like those of moles among quadrupeds, and, as 

 in the latter, indicate probably great power of propulsion in the fore 

 limbs. The finger bones were long and slender and formed a long fin 

 or flipper, while the upper arm was probably concealed in the skin. 

 The whole limb came off but a short distance posterior to the head. 



These reptiles, so far as known, were all carnivorous ; their food was 

 chiefly fishes. Some of the species on which they preyed are enumer- 

 ated in the portion devoted to them, and their structural characters 

 pointed out. 



As it is desirable to develop the science of geology, the writer would 

 be glad if his" friends in the West would forward to him, in Philadelphia, 

 at his expense, specimens of bones or teeth which they may find. He 

 will return to them determinations of their nature, ami credit them 

 with discoveries which may result from their care and interest in pre- 

 serving them, in the publications of scientific bodies. 



SAUROPTERYGIA. 



POLYCOTYLUS, (COPE.) 



Trans. Amer. PMlos. Soc, 1869, p. 34. 



This genus is established on a series of vertebrae with portions of 

 pelvic arch and posterior extremity, discovered in the upper cretaceous 

 of Kansas by W. E. Webb, superintendent of the land office in Topeka, 

 Kansas. The point at which the remains were found is about five miles 

 west of Fort Wallace on the plains near the Smoky Hill Eiver, Kansas, 

 in a yellow cretaceous limestone. 



The animal thus indicated is of interest in American vertebrate paleon- 

 tology, as the first true Plesiosauroid determined within our limits. 

 That its affinities are nearer to Plesiosaurus than to Elasmosaurus will 

 be apparent from the following description. 



There are wholes or portions of twenty-one vertebrae, of which but 

 two retain their neural arches, and six are represented by neural arches 

 only. Four centra may be referred to the caudal series, the remainder 



