BRITISH FOSSIL REPTILES. 7^ 



The humerus, or femur, is remarkable for its thickness, whence 

 the specific name proposed for this species ; its distal flattened 

 extremity is one inch and a half thick, the breadth of the same 

 part being only four inches and a half, and the lengtli of the 

 entire bone nine inches and a half. The contour of the head is 

 transversely oval. The central part of the bone is occupied by 

 a coarse cellular structure, one inch and a half in diameter, 

 surrounded by dense osseous walls three lines thick. 



The body of a cervical vertebra of this Plesiosaurus measures 



Inches. Lines. 



in longitudinal diameter 1 7 



in transverse 2 .3 



in vertical 1 9 



The distance between the neurapophysial 



and costal pits is 1 : 



the form of the costal pit is a full transverse ellipse, and there 

 is a transverse depression about three lines in length in the 

 centre of the articular surface of the body. The neurapophysial 

 pits are much wider in the dorsal than in the cervical vertebrae. 

 The sides of the vertebrae are smooth and slightly concave. 



Plesiosaurus arcuatus. 



Under this name I designate a species of Plesiosaurus, of 

 which I have been able to study parts of the skeleton in the 

 British Museum (from the collection of Mr. Hawkins), in the 

 Bristol Museum, and in the collections of Lord Cole and Prof. 

 Sedgwick. 



The vertebrae, especially those at the posterior moiety of the 

 cervical region, are characterized by the development of distinct 

 transverse processes from the sides of the centrum for the sup- 

 port of the cervical ribs. These processes have the articular 

 surfaces traversed by a longitudinal groove, as in other Plesio- 

 sauri, and consequently thus present the appearance of the two 

 normal transverse processes confluent at the base. The arti- 

 cular surfaces on the anterior and posterior sides of the body of 

 the vertebra present the true Plesiosaurian character, being 

 slightly concave with a gentle central convexity. The lateral 

 and inferior surfacesof the vertebral centre are smooth and con- 

 cave. Theneurapophysis from its base to the summit of its oblique 

 process is equal in vertical extent to the rest of the vertebra 

 below : the inner surface of the neurapophysis is traversed in 

 its middle by a longitudhial ridge, (at least in the posterior cer- 

 vicals,) probably for the attachment of the membrane of the 

 spinal cord. The spinous process of the neurapophyscs is high 



