26 



PERMO-CARBONIFEROUS VERTEBRATES FROM NEW MEXICO. 



oval in outline, a little higher than wide, and the pubes present broad faces tri- 

 angular in outline and slanting inward, downward, and forward, but the anterior 

 ends of the bones are horizontal (fig. 13, c), so that at the base of the broad faces 

 there is a flat shelf, perhaps slightly indented at the median line where the two 

 bones meet. 



The ischium is longer than the pubis, extending posterior to the acetabulum 

 almost twice as far as that bone does anterior to it. The upper margin begins 

 near the upper posterior edge of the acetabulum and runs backward and down- 

 ward in a concave line. The posterior part of the margin turns downward 

 and joins the posterior border in a sharp angle; this border is nearly straight and 

 passes sharply inward, downward, and a little forward. The union of the bones 

 of the two sides leaves a notch at the posterior end of the pelvis. As in the pubis, 

 the main portion of the bones is horizontal below the acetabulum, but the inner 



Fig. 14. — Diasparactus zenos Case, X yi. A, posterior view of right femur; 

 B, posterior view of left femur; C, anterior view of left femur. 



edges turn down sharply and meet in a median symphysis, which finds expression 

 on the lower surface in a sharp keel, continuous with that formed by the pubes. 

 With the exception of the prepubic faces, never seen by us before but described 

 by Broili in a specimen of Diadectes from Texas, now in Munich, the whole pelvis 

 differs very little from those of the specimens of Diadectes already known and 

 closely resembles that of Limnoscelis and Seymouria. 



We are unable to explain the meaning of the peculiar shelf on the outer side 

 of the crest of the ilium. In Diadectes the upper ends of the neural spines, in 

 the dorsal region, are broad and rugose and, in some cases, even expanded; this 

 has led Case to make the suggestion that there might have been an imperfect 

 dorsal armor, such as occurs in Pareiasaurus, and that the shelf may have been the 

 place of contact with the lower end of a broader plate, or plates, covering the pelvic 

 region. No trace of any dorsal armor has been discovered in any specimen of the 

 family. In Diasparactus the dorsal spines, as described below, are higher than 

 in any other known genus of the family and there is no distal expansion or rugosity 

 of the spines ; the shelf is fully as well developed, however, as in the genus Diadectes. 



