58 MAEINE EEPTILES OF THE OXFOED CLAY. 



the strongly-developed tuberosity, the oblique proximal face of which is flat and 

 roughened for cartilage. The shaft is oval in section, widening gradually towards the 

 distal expansion ; the anterior border is nearly straight, while the posterior is concave, 

 the widening being mainly postaxial. The ventral and postaxial face of the upper 

 part of the shaft is greatly roughened for muscle-attachments. Distally the bone is 

 much flattened, and the expanded portion is rather more clearly marked off from the 

 shaft than is the case in Pliosaurus. There are articular surfaces for the radius and 

 ulna, but behind that for the latter bone there is a free border which in life was edged 

 with cartilage and may have supported a postaxial accessory ossicle. 



The radius (text-fig. 23, A, r.) is about as long as it is broad. It articulates with the 

 humerus by a nearly straight facet. Its outer (anterior) border is convex, the inner 

 (postaxial) is concave and appears to have enclosed with the ulna a small vacuity. 

 Distally there is a long straight facet for the radiate (rad.) and a short oblique one for 

 union with the intermedium (int.). The ulna (u.) is smaller than the radius, and is 

 rather wider than long. Its proximal (humeral) border is slightly convex, its inner 

 (preaxial) edge is concave, the outer strongly convex ; distally it bears facets for union 

 with the intermedium and ulnare. The form and arrangement of the carpals and the 

 digits will be best understood from the figure. The fifth metacarpal, as usual, 

 articulates proximally with the ulnare (uln.). The metacarpals are much flattened, 

 as also are the proximal phalanges, while the distal phalanges become more rounded ; 

 all the phalanges are strongly constricted in the middle. The number of phalanges in 

 each of the five digits is not known. 



Pelvic Girdle (text-fig. 24). — The pelvis, as in the other Pliosaurs, is remarkable for 

 the large size of the ischia and pubes. The pubis (pu.) is a large oblong plate of thin 

 bone, uniting with its fellow on the middle line in a long symphysis, and with the 

 ischium by a small facet. The inner edge is for the most part straight, but in front 

 curves outwards, passing into the strongly convex anterior border, which is grooved 

 and was fringed with cartilage in life. The outer edge is concave, but there is a slight 

 antero-external prominence where it joins the anterior border. The acetabular surface 

 (acet.) is large and gently concave, and is continuous internally with the ischial facet. 

 The region of the bone bearing these facets is considerably thickened, the thickening 

 extending across to the symphysial border. The posterior border is concave, forming 

 the anterior edge of the obturator foramen (obt.f.), which was not closed by bone, but 

 was probably completed internally by the bar of cartilage uniting the pubic with the 

 ischial symphysis. 



The ischium (is.) is remarkable for its great posterior prolongation. It consists of 

 a head which bears three facets, one forming the middle portion of the acetabulum, 

 the others for the pubis and ilium. Internal to this it narrows into a slight neck, then 

 widening out into the great ventral plate, the form of which is shown in the figure. 

 The two ischia unite in a very long median symphysis, diverging from one another 



