METEIOEHYNCHUS. 



175 



border of the ilium and a smooth concave facet forming the lower part of the 

 acetabulum. The anterior process {a.p.i.) is nearly circular in section and terminates 

 in a convex surface which bears no clearly defined facet for either the ilium or the 

 upper end of the pubis ; probably much cartilage was developed in this region. 



The pubis (pu., text-figs. 71, 72) is shorter and stouter than in Steneosaurus : 

 in individuals in which ossification is far advanced there is a moderately long 

 straight pubic symphysis, in front of which the bone was fringed with cartilage. The 

 neck is less slender than in Stc7ieosaurus. The upper end is usually much crushed, but 

 in a specimen of Mdriorhynchvs cultridens (R. 3804) it terminates in an elongated oval, 



Text-fijr. 72. 



sac.s.z 



sac.s.i 



sym.is 



sympi 



Inner (sacral) side of left half of pelvis of Metriorliyncltus moreli. (R. 2054, | nat. size.) 

 a.a., anterior angle of ilium; a.p.i., anterior process of ischium ; ih, ilium; is., ischium; pu., pubis; 

 sctc.s.l, sac.s.2, surfaces for union with the first and second sacral ribs; sym.is., symphysial surface 

 of ischium ; sym.pu., symphysial surface of pubis. 



slightly convex surface, which seems to have been covered with cartilage and probably 

 articulated with the ilium. Continuous with the postero-internal side of this there is 

 a small oblique facet which may indicate an articulation with the anterior process 

 of the ischium, but unfortunately this bone is imperfect in the skeleton in question. 



On the whole, it appears from the relatively small size of the ilium and from the 

 weakness of its union with the slender sacral ribs, that the great development of the 

 caudal fin has, to some extent, superseded the hind paddle as a means of propulsion, 

 at least as compared with the condition found in Steneosaurus. 



