BRITISH FOSSIL RKPTILES. 'Jl 



The head is shorter in proportion to its breadth than in any 

 of the previously described Plesiosauri; whence the specific name 

 proposed for this species. 



There are twenty-six teeth on each side of the lower jaw, the 

 terminal portion of which is less abruptly expanded than in the 

 PL grandis or arcuatus. One of the large anterior teeth of 

 this species measures one inch and a half in length and one 

 third of an inch in breadth ; its transverse section is nearly cir- 

 cular. The crown of the teeth is sculptured with well-marked 

 and finely- waved longitudinal grooves. 



The breadth of the distal end of the humerus equals half the 

 length of the bone, which is nine inches ; the form of that bone 

 is the same as in the PL macrocephalus. The other bones of 

 the anterior paddle are not sufficiently complete to aid in cha- 

 racterizing the present species. In the posterior extremity the 

 ischium differs from both that of PL doUchodeirus and PL Haw- 

 Idnsii in the greater width and less deep concavity of its anterior 

 margin ; from which may be inferred a corresponding modifica- 

 tion of the pubis, where that bone combines with the ischium 

 to complete the abturator foramen. The mesial margin is more 

 convex than in the PL Haivkinsii. 



The femur is a tenth part longer than the humerus, and its 

 distal extremity is relatively less expanded : its anterior margin 

 is less concave than in the PL macrocephalus. It measures 

 nine inches nine lines in length. 



The tibia is somewhat narrower and its anterior and posterior 

 margins less curved than in the PL macrocephalus. The 

 fibula approaches more nearly in form to that of the PL ma- 

 crocephalus than to the fibula of any other species of Plesio- 

 saurus ; but its tibial margin is more extended and less deeply 

 (ton cave. Its breadth is equal to its length, which is only two 

 lines less than that of the tibia. The tarsal bone next the in- 

 terspace of the tibia and fibula is not emarginate. 



The total length of the skeleton of the PL hrachycephalus 

 from the Bitton lias is ten feet and a half. The length of the 

 head is one eighth of the entire length of the skeleton, or equals 

 tlie nine anterior cervical vertebrae. 



Localities. — The incomplete skeleton of this species in the 

 Museum of the Bristol Philosophical Institution was discovered 

 in the lias at Bitton, Gloucestershire, in 1830. 



Several vertebrae in the Gymnasium at Stuttgard, from the lias 

 of Boll, appear to belong to the present species. 



Vertebrae of the PL hrachycephalus also occur in the lias at 

 Whitby. 



