LIASSIC PLESIOSAURS. 19 



skeleton (Tab. V) is fourteen feet, which would be increased by several inches were 

 the tail entire and outstretched. 



The specimen of PL homahsjmiilijlus in the Museum of the Yorkshire Philosophical 

 Society is larger than the one in the British Museum, but has been lithographed on a 

 smaller scale in Tab. VIII; it measures IG feet 6 inches in total length. It lies in a 

 somewhat similar posture to that in the British Museum, but with the long and 

 slender neck and anterior dorsals bent so as to give a concavity to the dorsal con- 

 tour of the animal ; the caudal vertebrae, which are better preserved, are also bent in 

 the same direction, and all the vertebras follow in their consecutive undisturbed 

 jiixta-position in both skeletons. The numbers of the vertebrae in the cervical and 

 dorsal series respectively appear to be the same. The diapophysis has got entire 

 possession of the rib at the fortieth vertebra, counting from the head ; and the costal 

 surface begins, with its process, to sink again upon the centrum, at the sixty-seventh 

 vertebra, which the thickness of the diapophysis indicates to be a sacral vertebra. 

 Beyond this may be counted twenty-seven caudal vertebrae, and it is not probable 

 that their number exceeded thirty. 



The cervical vertebrae show the same distinctive characters of the species which 

 have been already defined ; the neural spine is preserved in a much greater proportion 

 of the cervical series ; in the fifteenth cervical it shows a height of two inches, and a 

 nearly equal antero-posterior breadth ; with a broadly truncate summit, having the 

 angles rounded off. The vertebrae keep their proportion of length from this point to 

 the end of the dorsal series ; they then grow shorter to the end of the tail, throughout 

 the greater part of which the centrum is deeper, and the neural spines longer and 

 narrower, than in the neck, indicative of the greater mass of muscle operating on the 

 tail, and also its greater flexibility in a given extent. The costal series has suffered 

 much more displacement and loss in the York specimen than that in the British 

 Museum; the larger ribs are a good deal jumbled and broken in the region of the 

 trunk or thoracic abdominal cavity, but they show the same massive character. The 

 ischio-pubic part of the pelvis has been drawn away, at an acute angle, from the ilium 

 and sacrum; its inner or upper surface is exposed at 63, Qh Tab. VIII. The right 

 pelvic limb has been moved forward, with the head of the femur lying upon the lower 

 end of the right coracoid. The right pectoral limb extends forward from near its 

 normal place of articulation with the coracoid ; but it has been turned bodily over, 

 showing its inner or palmar surface. The limbs of the left side are huddled in a dislo- 

 cated and incomplete state beneath the hinder part of the trunk. 



The presence of both these limbs, in an excellent state of preservation, supplies the 

 chief deficiency in the specimen in the British Museum previously described. 



The pectoral limb, as in PI. clolichoddms, is rather shorter than the pelvic one ; 

 its entire length is 3 feet 8 inches, equalling sixteen vertebrae towards the base of the 

 neck. The humerus, 13 inches in length and 7^ inches in distal breadth, is broader 



