BRITISH FOSSIL REPTILES. 7-3 



articular surfaces is nearly equal to the vertical diameter of the 

 latter. The costal pits are slightly raised above the surround- 

 ing surface ; they are of a transversely elliptic form, and with a 

 greater vertical breadth than usual ; they are also separated by 

 a deeper and wider channel than in the PL Hawkinsii. The 

 under sm-face of the vertebrae is traversed along its middle by a 

 smooth broadish ridge, on each side of which is the charac- 

 teristic foramen, of an elliptical form. The longitudinal ridge 

 disappears in the dorsal vertebrae. The sides of the neurapo- 

 physial depressions meet at nearly a right angle. The spinous 

 process is less extended in the antero-posterior direction than 

 in the PL macroceplmlus, but is thicker (transversely) than in 

 the PL doliclwdeirus. 



The dorsal vertebrae are a little shorter than the cervical : 

 they have the same anterior and posterior articular surfaces ; 

 but the lateral surfaces are smoother and more concave. In 

 the caudal vertebrje the inferior surface of the centrum is flat- 

 tened : the hsemapophysial pits are well marked, especially the 

 anterior part. The humerus of this species has the same form 

 as the bone of the Plesiosaurus figm-ed by Mr. Conybeare in 

 the 1st Vol. 2nd Series of the GeoL Trmis. pi. xxii. fig. 1 : it is 

 expanded immediately below the head by the development of 

 two rough protuberances for the insertion of muscles : below 

 these the shaft of the bone continues to diminish gradually in 

 thickness and increase in breadth to its distal extremity. The 

 contour of the anterior and posterior margins resembles that of 

 the same parts in the PL doliclwdeirus , the anterior being 

 slightly convex, the posterior in a greater degree concave : the 

 distal extremity is bounded by a pretty regular convex curvature. 



The rough muscular surfaces on the inner side of the bone 

 near the proximal extremity are only slightly raised above the 

 smooth surrounding surface, and they are so close together as to 

 be nearly confluent. The external tubercle is as it were sepa- 

 rated by a compression from the general proximal surface. At 

 the distal extremity the rough articular surface is divided into 

 two parts by a shallow depression on the internal or sternal 

 side of the bone ; at the junction of the middle with the pos- 

 terior third of the distal curve. 



Inches. Lines. 

 The length of the humerus is ... 8 6 



The breadth of the distal end ... 3 10 



The radius presents the common form, is more expanded at 

 the proximal than the distal end, compressed, and with the an- 

 terior and posterior margins concave. The ulna is as long as 



