390 GEOLOGICAL SURVEY OF THE TERRITORIES. 



Inclics. 



Width parallelopiped phalange 1.2 



Thickness parallelopiped phalange 1. 2 



Thickness depressed phalange 1. 



Width depressed phalange 1.4 



Length depressed phalange 1. 9 



These powerful extremital pieces indicate a body to be propelled, of 

 not less than usual proportions. If this be the case the number of dor- 

 sal vertebras is considerably greater than in the species of this order in 

 general, and approaching more the Ichthyosauri. I do not intend to 

 suggest any affinity between the latter and the present genus, as none 

 exists. What the extent of cervical vertebras may have been is uncer- 

 tain. The caudals have probably been numerous, though not probably 

 so extended as in Elasmosaurus. 



The size of the species can be approximately estimated from the pro- 

 portions furnished by Owen (Reptiles of the Liassic Formations) for 

 Pleslosaurus rostratus. The skeleton of this species measures eleven 

 feet eight inches, and the dorsal vertebras are of less vertical and equal 

 transverse diameter compared with those of the present saurian. We 

 may therefore suppose that the latter exceeded the former in dimen- 

 sions. 



William E. Webb, of Topeka, discovered the specimens from which 

 this species was first described, and liberally forwarded them to me for 

 examination and description. Other specimens have been discovered 

 since that time by various other persons. I have received numerous 

 fragments of an individual of about the size of the one above described, 

 which were found by Professor B. F. Mudge, at a point near the mouth 

 of the north branch of the Smoky Hill Eiver. 



These consist of a few vertebras, portions of pelvic and scapuiar 

 arches, and three proximal bones of the limbs. Which of these is 

 femur and which humerus I am unable to determine, owing to their 

 close resemblance. The vertebras do not differ from those of the speci- 

 men just described. The limb bones are stout and expanded and 

 thinned distally; this thinning is remarkable and indicates a much- 

 ilattened metapodial region. The head is slightly expanded, the artic- 

 ular face being turned obliquely to the inner face of the shaft; the surface 

 is pitted for attachment of the articular cartilage ; two-fifths the length 

 from the proximal end is an extensive and exceedingly rugose surface, 

 as wide as the shaft, for the insertion of the adductor muscles. 



M. 



Diameter of centrum of lumbar vertebras 0. 08 



Length (?) humerus 0. 45 



Diameter head 0. 125 



Diameter shaft. . . .- 0. 098 



Diameter distal end (transverse) restored in part 0. 18 



Should the humerus have been related to the fore limb as in Plesio- 

 saurus dolichodirus, Conyb., the latter would have had a length of four 

 feet three inches; as the proportions of the radius and phalanges are 

 shorter, the limb was probably relatively shorter. If related to the 

 total length, as in the same Plesiosaur, the humerus would indicate a 

 length of seventeen and a half feet. As the cervical vertebras become 

 attenuated as compared with the dorsals to a greater degree in Poly- 

 cotylus than in Plesiosaur us, I have little doubt that the length of this 

 species exceeded that amount. 



