W. R. Smellie — A New Oxford Clay Plesiosaur. 341 



III. — On a New Plksiosaur from the Oxford Clay. 



By William E. Smellie, M.A., B.Sc, Hunterian Museum, Glasgow 



University. 



TMHIS Plesiosaur was collected from the Oxford Clay at Peterborough 

 1_ by A. IS". Leeds, Esq., F.G.S., and was acquired for the Hunterian 

 Museum, Glasgow University, by Professor J. W. Gregory. The 

 specimen has many striking resemblances to CryptocJeidus oxoniensis, 

 but detailed examination showed that it could not belong to that 

 species, and the differences existing in the paddle, shoulder-girdle, 

 number of vertebrae, and conditions of ossification are such that it 

 cannot be retained in that genus as now defined. The paddle closely 

 resembles that of Tricleidus, but the shoulder-girdle alone is sufficient 

 to prevent the inclusion of the specimen in that genus. It seems 

 advisable to create a new genus, and as it may be some time before 

 a full description can be published a preliminary account is here given. 



Apractocleidtts, gen. nov. 1 



Plesiosaurs in which the neck is composed of about twenty-nine 

 vertebrae of which the centra are wider than high and slightly higher 

 than long. The oval articular ends are concave in the centre but 

 convex near the margin. There are three pectoral vertebrae and 

 twenty-three dorsals, or two pectorals and twenty-four dorsals. The 

 shoulder- girdle is of Elasmosaurian type and so ossified as to form 

 a very rigid structure. The coracoids are exceptionally broad and 

 the postero-lateral processes are greatly produced. The dorsal rami 

 of the scapula? are widely extended in a similar fashion. The ventral 

 ramus of the scapula is large, and in the adult the anterior portion 

 has grown forward beyond the clavicles, which are very thin films 

 of bone lying wholly within the visceral surface of the scapulae. 

 A rudimentary interclaviele may be present. In the mid- ventral line 

 the scapulae and the anterior parts of the coracoids impart a slightly 

 carinate appearance to the shoulder-girdle. The humerus is greatly 

 expanded distally and articulates with four elements. The pelvis is 

 of great breadth, and the wide spread of the antero-external angles 

 of the pubes taken in conjunction with the breadth of the shoulder- 

 girdle indicates a genus of exceptionally broad build. The femur is 

 slightly smaller and more slender than the humerus, and is not 

 greatly expanded distally. 



The genus is represented by one species, Jpractocleidus teretipes, 

 n.sp., the specific name (from teres = rubbed, well-chiselled, elegant, 

 and pes = a foot) being descriptive of the symmetrical outline of the 

 paddle. 



In the type-specimen the parts preserved form a large portion of 

 the skeleton of a fully adult individual, and the state of preservation 

 of the bones is remarkably perfect even for Oxford Clay fossils. 

 It differs from Cryptocleidus oxoniensis in the number rather than the 



1 The name Apractocleidus, meaning idle or functionless clavicle, has been 

 adopted to accord with the names of the related genera Tricleidus and 

 Cryptocleidus. For the suggestion of the name I am indebted to the 

 Eev. Gavin Warnock, B.D. 



