ROOM III. PLESIOSAURIAN REMAINS FROM THE WEALDEN. 351 



vertebrae are shorter than in the species previously described, 

 and approach in their proportions to those of the Ichthyosau- 

 rus : the processes of the cervical vertebrae are stronger. 



The dorsal vertebrae differ from those of P. Hawkinsii in 

 the bodies being more flattened antero-posteriorly, and more 

 concave laterally. Other osteological characters, establishing 

 the specific distinction of this Plesiosaurus, are minutely de- 

 tailed in the Reports so often cited. 



PLESIOSAURUS RUGOSUS. Wall-case D. This specimen of a 

 very rare species of Plesiosaurus was discovered in the Lias 

 near Belvoir Castle, and presented to the British Museum by 

 the Duke of Rutland. It consists of the cervical region of 

 the vertebral column, a considerable portion of the bones of 

 the trunk, those of the four paddles, and some of the vertebrae 

 of the tail ; but the latter are much displaced. The cranium 

 is wanting. 



Some detached Plesiosaurian vertebrae, readily distinguished 

 from all others by the peculiarly rugous character of the free, 

 or non-articular surfaces of the body, were ascribed to a dis- 

 tinct species, under the name of P. rugosus, in " Brit. Rep." 

 1839 ; and other characters of these isolated bones were 

 pointed out. 1 The discovery of the skeleton before us has 

 confirmed the accuracy of the distinction. 



Among other peculiarities, Prof. Owen remarks, that the 

 two costal impressions on each side the bodies of the middle 

 cervical vertebrae are in this species completely divided, and 

 by a wider and deeper groove ; and they are situated near the 

 lower margin of the vertebra. The contour of the articular 

 surface of the vertebral body is almost circular, the peripheral 

 border being convex, and leading inward to a concavity, and 

 the centre of this surface is slightly convex. 



The absence of the cranium, and the dislocated state of the 

 spinal column, together with the loss of many of the vertebrae, 

 render it useless to give a more particular description. 



PLESIOSAURIAN REMAINS FROM THE WEALDEN. Among the 

 reptilian bones discovered in the strata of Tilgate Forest, were 

 dorsal and cervical vertebrae of Plesiosauri, referable to one of 

 the typical species previously described : probably the P. doli- 

 chodeirus : some of them are figured in my " Fossils of Til- 



1 " Brit Assoc. Rep." 1839, p. 82. 



