G10 



WILLIAM R, SMELLIE ON 



The genus is represented by one species, Apractocleidus teretipes, n. sp., the 

 specific name (from teres = rubbed, well-chiselled, elegant, and pes = & foot) being 

 descriptive of the symmetrical outline of the paddle. 



In the type specimen the parts preserved form a large portion of a fully adult 

 individual, and the state of preservation of the bones is remarkably perfect even for 

 Oxford Clay fossils. The head, unfortunately, is absent, but the vertebral column, 

 ribs, shoulder and pelvic girdles, and fore and hind limbs are all well represented. 



Vertebral Column. 



The bones present comprise the atlas and axis and other twenty-seven cervical 

 vertebrae — three pectorals, twenty-three dorsals, and one sacral. All posterior to the 



a b c 



.nip.. 



-.n.sfi 



ax.c 



aw. lr 



Text-Fig. 1. 



Atlas and axis of Apractocleidus teretipes : A, from front ; B, from right side ; C, from behind. (Type specimen V. 1091, nat. 

 size.) at. a., neural arch of atlas; a.w.b., anterior wedge-bone; ax. a., neural arch of axis; ax.c, centrum of axis; 

 hy.r., hyapophysial ridge; n.c, neural canal ; n.sp., neural spine; od., odontoid; p.z., posterior zygapophysis ; r.„ rib 

 of atlas ; r.t, rib of axis. 



first sacral are missing. From the atlas to the sacral the series seems complete, and, 

 while it is not impossible that the neck lacks its full complement, it is certain that 

 pectoral and dorsal regions show no missing vertebra,. and it seems a sound assump- 

 tion to consider the series complete as far as it goes. 



The atlas and axis (text-fig. 1, A, B, C). — The various bones composing the atlas 

 and axis are so completely fused in the specimen that it is with the greatest difficulty 

 and uncertainty that the sutures can be even partially traced. In the atlantal cup 

 the sutures between the anterior wedge-bone (a.tv.b.) and the odontoid (od.), and 

 between the odontoid and the lateral pieces of the neural arch of the atlas (at.a.), are 

 almost obliterated. The cup itself is deeply excavated and smooth, and, in section, 



