THE UPPER TRIASSIC OF WESTERN TEXAS. 



73 



where it fits into the deep pits on the inner side of the ilium. There is a notch on the 

 posterior side near the proximal end which is in opposition to a similar notch on the 

 anterior side of the proximal end of the second rib, leaving an opening for the escape 

 of the nerves between the two vertebrae. The anterior rib slightly overlaps the posterior 

 rib at the distal end. 



The second rib is nearly as large at its origin as the anterior one, but the neck is 

 somewhat narrower, due to the presence of notches on the anterior and posterior edges. 

 Its anterior edge slants somewhat forward, but not at so great an angle as the posterior edge, 

 which extends back to the extremity of the posterior process of the blade of the ilium. 

 The distal end is not so much thickened as in the anterior rib, and the posterior portion 

 of the distal end attaches to the ridge on the inner side of the ilium by an overlap. 



Specimen No. 7470 consists of the nearly entire right half of the pelvis, with the 

 two sacral vertebras and several associated dorsals. It was found by the author near 



FIG. 28. 



A. Upper surface of pelvis and sacrum, No. 7266, U. of Mich. 



B. Right side of pelvis, No. 7470, U. of Mich. X 0.25. 



X 0.25. 



the head of Holmes Creek, Crosby County, Texas. The posterior half of the ilium has 

 been slightly crushed down and out, and the distal portion of the pubis is lacking, but 

 the ischial portion of the symphysis is complete and a part of the ischium of the left 

 side is preserved. 



The form of the ilium (fig. 28 B) is most like that of No. 7322. The anterior process 

 is long, reaching as far forward as the articulation with the pubis, and the distal end is 

 slightly but definitely down-turned. There is no buttress over the anterior portion 

 of the upper edge of the cotylus. The posterior process is somewhat distorted by the 

 crushing described above, but it is apparent that its lower edge rose rather abruptly, 

 much more so than in No. 7322. 



The upper edge of the blade of the ilium is decidedly thickened, more at the anterior 

 and posterior ends, but also in the median portion. The top of the anterior process is 

 wide and only slightly convex. Near the extremity of the posterior end there is a very 

 decided thickening of the bone, due to the development on the outer face of a triangular 

 prominence resembling the buttress which is described upon specimens 7333 and 7266, 

 but at the opposite end of the blade of the ilium. The cotylus is very deep in the anterior 



