7o 



humerus, I am unable to delcrmiiic, owing to their close resemblance. The 

 vertebra; do not (liUcr i'rom tliose of the specimen just described. The limb- 

 bones are stout and expanded, and thinned distally ; this thinning is remark- 

 able, and indicates a much flattened metapodial region. The head is slightly 

 expanded, the articular face being turned obliquely to the inner face of the 

 shaft ; the surface is pitted for attachment of the jirticular cartilage ; two- 

 fiflhs 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. 



Measurements. 



M. 



Diameter of the ceutrum of tho lumbar vertebra 0.08 



Leugtb of tbe (?) humerus 0. 4.'> 



Diameter of tbe be.ad 0. liS 



Diameter of tbe sbaft 0. 098 



Diameter of the distal eud (transverse), restored in part 0. 18 



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

 saurus dilichodirus, Conyb., the latter would have had a length of 4 feet 

 3 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 Plesio.saur the humerus would indicate a length of \lh feet. The cer- 

 vical vertebrae become attenuated, as compared with the dorsals, to a greater 

 degree in Polycotylux than in Flesiosaurus. 



ELASMOSAURUS, Cope. 



This genus has been more completely preserved to us than any oilier 

 American representative of the order. In the interpretation, however, con- 

 siderable care is necessary, as the form appears, at first sight, to reverse, to 

 a remarkable degree, the usual proportions of known reptiles. The scapular 

 arch, in the absence of the episternum, presents the same number of ele- 

 ments as the pelvic, and is not without resemblance to the latter, as it 

 exists in some species of the order. The fortunate preservation of the series 

 of cervical vertebraj shows this to have been, in the typical species, three 

 times the lenglii of the body; much exceeding in this disproportion that 

 knowu to exist in other species of the order. 



The neural arches are everywhere continuous with the centra, witiiout 

 sign of suture, and are externally plane. The nenial canal is exceedingly 

 small for the size of tlic vertebra;, especially on the lumbar and caudal verte- 

 br;e. 



