74 



MAEINE EEPTILES OF THE OXEOED CLAY. 



in proportion to their width than in the other species ; the chevron-facets on the 

 caudals are large. 



A number of peculiarly shaped bones (text-fig. 29), preserved with this skeleton, 

 are here regarded as sacral or anterior caudal ribs. At their proximal end they 

 bear a head (/*.) with two facets for union with the lower part of the neural arch and 

 with the centrum ; distally they expand into a broad blade, which curves somewhat 

 downwards and is strengthened on the ventral surface by a ridge (r.) running out 

 from the head. They vary in form at their outer ends : in some there is a large 

 terminal facet, perhaps for union with the ilium ; in most the outer end is produced 

 forwards and backwards into a short process terminating in a flat facet (/.), which 

 probably united with the corresponding facet on the rib before and behind. This 

 arrangement would add greatly to the rigidity of the sacral and anterior caudal regions, 

 a condition probably connected with the great development of the hind paddles. 



Text-fig. 29. 



Sacral ribs (?) of Pdoneustcs evansi : A, B, from above ; C, from below. (E. 3891, | nat. size.) 

 /., facet for contact with next rib ; 7i., articular head ; ?•., strengthening ridge. 



Of the pelvis only the ilia are preserved. These expand dorsally into a broad 

 triangular blade much as in Pliosauras, and, as will be seen from text-fig. 25, B, 

 in Peloneustes philarchus also. The upper border is greatly roughened and bears a 

 surface probably for union with the outer end of one or more of the expanded ribs 

 noticed above. The upper part of the outer face of the posterior border has a 

 strongly developed rugosity for muscle-attachment. 



The fore and hind paddles are much the same as in Peloneustes philarohns, except 

 that the distal expansion of the humerus and femur is perhaps a little more marked, 

 and the femur a little larger iu proportion to the humerus. 



