MERHTAM: TRIASSIC 1 TCHTIIYOSAl'RIA. 



55 



considered as representing a quite different reptilian group. This is particu- 

 larly true of the two inferior elements, which are much broadened, and show 

 the expanded plate-like form seen in some of the most primitive reptilian types. 

 The ilium as known in Torctonicmus (fig. 69) appears to be considerably 

 elongated and is relatively slender. In Ci/niboKi>oii(lifltin (fig. 70) the ilium is 

 somewhat shorter and is considerably expanded distally. As seen in specimen 

 9950, in which the elements of the pelvic arch seem to have held together, the 



67 



68 



69 



Fig. 67. ProcoJo/ilion trigoniceps Owen. Pelvis, natural size. (After Broom.) Pu, pubis; Is, 

 ischium; O.f., obturator foramen. 



Fig. 68. Stereosternwm tumidum Cope. Pelvis, natural size. (After Osborn.) Pu, pubis; Is, isch- 

 ium ; O.f., obturator foramen. 



Fig. 69. Toretocnemus calif ornicus Merriam. Pelvis, natural size. Pu, pubis; Is, ischium; //, 

 ilium ; O.f., obturator foramen. 



ilium is turned forward at the proximal end. Nearly the same form of ilium 

 is present in Delphinosaurus (fig. 72) and Shastasaurus (fig. 73). In DelpM- 

 iiosaurus there is on the posterior side, near the proximal end, a small tubercle 

 which does not appear in any of the other forms, and reminds one of the ante- 

 rior extension of the upper portion of the ilium in land or shore forms with 

 a strong sacral attachment. 



All of the Triassic genera agree in the broad expansion of the distal portion 

 of the pubis, but there is among them a considerable variation in the form of 

 the proximal end of the bone. According to Repossi (1902, tav. 9, fig. 3), in 

 Mijcosdiirns (fig. 71) the strongly curved median margin of the pubis bends 

 into the proximal end of the bone without the formation of a hook, and there 

 appears to be no opening corresponding to the obturator foramen. In Tore- 

 tocnemus the pubis is very broad proximally as well as distally, and is perfor- 

 ated by an obturator foramen. In Cymbospondylus an obturator foramen 

 may be present as in Toretocnemus. In some cases the opening may possibly 



