60 REPORT — 1839. 



In the hinder extremity the bones of the pelvic arch first 

 claim attention. The ileum is flattened and slightly expanded 

 at its superior free extremity, where it rests upon the sacral 

 ribs; its length is equal to four of the contiguous vertebras. 

 The pubic bones are in the form of large square-shaped plates, 

 with the angles i-ounded off, and a deep smooth emargiuaiion at 

 their posterior edge, which is turned towards the corresponding 

 emargination of the ischium to form the 'foramen ovale.' The 

 outer and posterior angle is marked by the articular surface 

 contributed by the pubis to the formation of the acetabulum. 

 The antero-posterior extent of the broad pubic bone equals in 

 this species nearly four of the parallel vertebras. 



The ischia present the form of inequilateral triangles, and are 

 straighter at their mesial edges than are the pubic bones : they 

 present a concavity at each of the other margins ; which is 

 deepest at the shorter and anterior margin. The length of the 

 ileum exceeds that of the pubis. The extent through which the 

 median margins of the ischia are joined to each other exceeds 

 that in other species of Plesiosaur. 



The femur is more slender in the shaft than the humerus, but 

 is of the same length : its distal flattened extremity is less ex- 

 panded. 



The tibia and fibula are more nearly equal in length than are 

 the corresponding bones of the fore paddle ; the breadth of the 

 reniform fibula equals its length. There are at least five bones 

 in the tarsus of this species. That which is wedged into the 

 interspace between the distal extremities of the tibia and fibula 

 is characterized by a concave notch at its tibial margin. The 

 number of digital phalanges, in addition to the metatarsal row, 

 corresponds with that given in the description of the generic 

 type. 



Full-grown individuals of this species appear to vary from 7 

 to 7i feet in length. 



Localities. — The Plesiosaums HawJcinsii is most common 

 in the lias quarries near Street. It occurs at Lyme ; but is less 

 common there than the PL dolichodeirus and PL macroce- 

 phalus next to be noticed. 



Vertebrae of this species have been found in the lias at Weston 

 near Bath ; in the lias bone-bed at Aust-Clift' in the neighbour- 

 hood of Bristol, and in that of the Pyrton passage on the Severn. 

 I have not yet seen any specimens referrible to this species from 

 the lias of Whitby or from that of Boll in Wirtemberg. 



Plesiosaurus dolichodeirus. 



The admirable description and restoration of this species 



