AND PELVIC BONES OP PLIOSATJRUS EVANSI. 721 



internal concave margin about 7| inches long, which, with the 

 ischium, enclosed a foramen ; and a thick external area slightly 

 convex in length, about 1\ inches long and about 3| inches deep 

 in the middle. The inner half of this area presumably gave a 

 strong attachment to the ischium, while the outer half contribnted 

 with the adjacent surface of the ischium to form the articular cavity 

 for the femur. 



The inner margin of the bone, which adjoined the other pubic 

 bone in the median line of the body, has a length of about 21^ inches. 

 It is not straight, but subconvex, making an angular bend in the 

 middle, where for the length of about 7 inches the bone thickens 

 moderately to form an articular surface for union with the pubic 

 bone of the opposite side. 



The anterior margin is nearly straight, is 11 inches long, and 

 very thin. The greatest length of this bone, from the middle of 

 this margin to the posterior angle of the articulation for the ischium, 

 is 22 inches. 



The external margin is about 4 inches shorter. It consists of: — an 

 anterior portion 10 inches long, convex in outline from front to back, 

 and terminated by a cartilaginous margin ; and a posterior portion 

 concave from front to back, which terminates in a perfectly ossified 

 rounded border : these two portions make an angle with each other. 



The surface of the bone is evenly flattened, except at the inner 

 posterior corner, where it is conspicuously compressed. 



There is a close correspondence in form between this bone and 

 the still larger pubic bones of Pliosaurs from the Kimmeridge Clay 

 of Ely. 



The Ischium (figs. 7-9). 



This bone when found was a good deal crushed ; and coming to 

 the Woodwardian Museum at a time when I was absent, no record is 

 available of the outline of the very thin broken posterior portion, 

 the preservation of which was found by Mr. Keeping to be imprac- 

 ticable ; but I should infer that the missing portion completed a 

 hatchet-shaped outline (fig. 7). As preserved the extreme length of 

 the bone is 18 inches ; when perfect, I estimate its extreme length, 

 in the median line where the ischiac bones joined each other in a 

 straight union, to have been about 23 inches. Its greatest posterior 

 width was about 20 inches, near to the hindermost border of the 

 bone ; the greatest anterior width is 13 inches, just behind the 

 femoral articulation. . Externally between these points the lateral 

 margin is deeply concave. At the articular surfaces for the femur and 

 pubis the bone becomes greatly thickened, as usual (fig. 8). The length 

 along these surfaces is 8 inches. The femoral area is the larger, 

 being 4 j inches long and 3| inches thick ; it is very slightly con- 

 cave in length, makes about a right angle with the adjacent posterior 

 lateral border, and makes a very large angle with the pubic articu- 

 lation, which is more compressed from above downward. 



The anterior margin is 9| inches from the pubic articulation to 

 the median suture of the body. This margin is concave externally 



