472 



PROF. W. J. SOLLAS ON PLESIOIAT7RTJS 



Notes on Plesiosaurus megacephalus, StutcJibury, and 

 P. brachycephalus, Owen. 



The type specimens of these two species are preserved in the 

 Bristol Museum ; so that I have had a good opportunity of making 

 a close acquaintance with them, and have succeeded in elucidating 

 some points in their anatomy which were hitherto obscure. 



Plesiosatjrtjs meoacephalus. 



1. The Roof of the Mouth. — The skull of this specimen lies on it3 

 dorsal surface, separated from its matrix from the snout to a trans- 

 verse fracture which traverses it across the orbits. The matrix 

 has been carefully chiselled away from between the rami of the 

 lower jaw, so as to clearly expose the roof of the mouth and the 

 base of the skull for its entire length. The anterior part of the 

 base (fig. 8), which lies in front of the fracture before mentioned, is 

 by a most lucky chance much better-preserved than that behind, and 

 thus affords us an opportunity which has long been desired of ascer- 

 taining more exactly the true nature of this part of the skull. 



Pig. 8. — Ventral View of the anterior Part of the Skull of 

 P. megacephalus. (Scale ^.) 



n, internal naris ; /, palatal foramen. 



It presents, about 2 inches behind the end of the mandibular 

 symphysis, two oval foramina (fig. 8, n) longer than broad (1*45 inch 

 in length) separated from each other by a bone which extends back- 



