74 NEW REPTILES AND STEGOCEPHALIANS FROM 



upper portion, but otherwise it is more shallow than in any other of the specimens; 

 this may be in part due to the distortion of the specimen. On the inner side there is a 

 much wider area above the place of the attachment of the distal ends of the sacral ribs; 

 the anterior rib was received into a deep rugose pit, as in specimen 7244, and the posterior 

 rib was attached along a ridge which ran backward from the pit. The anterior face 

 of the lower part of the ilium descends toward the articulation with the pubis much 

 more directly than in any other of the specimens. 



The ischium and pubis are closely anchylosed with the ilium, so that it is difficult 

 to follow the sutures. The anterior edge of the proximal portion of the pubis continues 

 almost directly downward from the articulation with the ilium; just below the artic- 

 ulation there is a large pit near the edge. A little below this, and in the lower part 

 of the cotylus, is the opening of the pubic foramen. The distal portion of the pubis 

 is lost. 



The posterior edge of the ischium runs downward and then turns sharply forward, 

 forming the upper edge of a narrow but strong process. The symphysis is preserved 

 forward almost to the juncture of the ischium with the pubis; the union of the bones of 

 the two sides is strong, as they meet in a wide articular face and are firmly fastened 

 together in the specimen. The line of the symphysis, so far as preserved, is sigmoid. 



The sacrum of this specimen is complete and resembles that of No. 7266. The 

 anterior rib rises from the level of the zygapophyses and is very heavy; the rib stands 

 with its greatest diameter vertically, which is perhaps the normal position. The distal 

 end was received in a pit on the inner side of the ilium. The two vertebrae are separate 

 and the zygapophyses between them are distinct and well formed. The neural spines 

 of the vertebrae are complete and show an enlargement of the upper end, forming heavy 

 flat tables which overhang the sides of the neural spine. The upper surface of the tabular 

 expansion is marked by a shallow depression which runs antero-posteriorly. 



In comparison with the pelvis of Rhytidiodon carolinensis, as figured by McGregor, 

 Nos. 7333 and 7266 are apparently of the same type and are probably Mystriosuchids, 

 but Nos. 7470, 7244, and 7322 are decidedly different. The ischium of No. 7470 resembles 

 that of R. carolinensis, but the posterior (upper) edge is perhaps a little more curved, 

 the symphysis is stronger, and the lower edge of the symphysis is sigmoid in outline. 

 There is no suggestion of a space between the ischium and pubis, filled during life with 

 cartilage; the two halves of the pelvis meet at a decided angle, and there could have 

 been little opportunity for a median vacuity. The pubis is largely lost, but the anterior 

 edge is decidedly convex in its upper portion, suggesting a very different contour from 

 that of R. carolinensis. These differences, combined with the shape of the ilium, suggest 

 that this pelvis belonged to some member of the Phytosaurid group, a suggestion borne 

 out by the few plates found with the specimen which are typically phytosaurian. The 

 peculiar outline of the upper part of the anterior edge of the pubis, suggesting a more 

 vertical position of the anterior face of the pubis, recalls the peculiar pelvis described by 

 Mehl, 1 from the Triassic of New Mexico, as Acompsosaurus wingatensis, and even more 

 the condition found in the Pseudosuchians Ornilhosuchus and Euparkeria. It is not 

 supposed that the resemblance implies genetic relationships, but so little is as yet known 

 of the Triassic reptiles in North America that note must be taken of suggested resem- 

 blances until their value may be correctly estimated. In v. Meyer's paper upon the 

 Reptilia of the Steuben Sandstone of the Upper Keuper 2 there are figured three phytosau- 

 rian ilia. Figure 1 has much the same form as Nos. 7333 and 7266, described and figured 

 above, while figure 5 resembles more closely No. 7244. Von Meyer did not assign the 

 ilia figured by him to any definite genus or species. 



1 Mehl, M. G., Quarterly Bulletin of the University of Oklahoma, new series, No. 103, p. 33, 1916. 



2 Meyer, H. v., Paleontographica, Bd. 7, Taf. 41, figs. 1, 3, 5. 



