164 MAEINE EEPTILES OF THE OXFOED CLAY. 



Genus CRYPTOCLEIDUS, Seeley. 

 [Proc. Roy. Soc. vol. li. (1892) p. 145, as a subgenus o£ Murcenosaicinis.'] 



Plesiosaurs in which the skull is relatively small, about a quarter the length of the 

 neck in the adult. Neck consisting of about 32 cervical vertebrae, the centra of which 

 are short, with oval articular faces which are deeply concave, at least in old individuals. 

 There are two or three pectoral vertebras and 21 or 22 dorsals. There seem to have been 

 three or four sacrals, the ribs of which are thickened and converge towards their outer 

 ends ; the number of caudals is uncertain, but probably was about thirty ; the posterior 

 caudals diminish in size rapidly. Cervical ribs with single heads, not much flattened, 

 and in some cases with a fairly prominent anterior angle. The ventral ribs forming a 

 strong plastron, each transverse row consisting of a median and three pairs of lateral 

 elements. Shoulder-girdle of the true Elasmosaurian type, the scapulse having an 

 extensive median symphysis continuous with that of the coracoids. Coracoids with 

 prominent postero-lateral processes in the adult. The clavicular arch consisting of two 

 triangular clavicles meeting in median symphysis : in some cases with a rudimentary 

 interclavicle interposed between them posteriorly (text-fig. 88) ; the clavicular arch, 

 except for its extreme anterior edge, lying entirely on the visceral surface of the ventral 

 bar of the scapula in the adult. The humerus greatly expanded distally ; radius 

 large, with an elongated anterior border, so that the axis of the expanded portion of 

 the paddle makes a slight angle with that of the humerus. In the pelvis the pubis 

 short in proportion to its width ; the femur not greatly expanded distally. 



Only a single species of this genus is recognised from the Oxford Clay of Peterborough. 



Cryptocleidus oxoniensis, Phillips, sp. 



[Plates IX. & X. ; text-figs. 78-94.] 



1871. Plesiosaurus oxoniensis, Phillips, Geology o£ Oxford, etc. p. 307. 

 1871. Plesiosaurus eurt/nierus, Phillips, op. cit. p. 315. 



1888. Plesiosaurus oxoniensis, Lydekker, Geol. Mag. [3] vol. v. p, 352. 



1889. Cimoliosawrus eurymerus, Lydekker, Catal. Foss. Rept. Brit. Mus. pt. ii. p. 205. 

 1889. Cimoliosaurus oxoniensis, Lydekker, torn. cit. p. 209. 



1892. Plesiosaurus durohrivensis, Seeley, Proc. Roy. Soc. vol. li. pp. 132-134 (for young). 



1892. Cimoliosaurus eumerus, Seeley, Proc. Roy. Soc. vol. li. p. 145. 



1892. Cryptocleidus platymerus, Seeley, torn. cit. p. 145. 



1895. Cryptocleidus oxoniensis, Andrews, Aun. Mag. Nat. Hist. [6] vol. xv. p. 335. 



Type Specimen. — Cervical, dorsal, and caudal vertebrse described and figured by 

 Phillips in the ' Geology of Oxford, etc.,' pp. 307-309, figs, cxiii.-cxv. Phillips also 



