PERMO-CARBONIFEROUS VERTEBRATES FROM NEW MEXICO. 



53 



plaster cast of the arm and hand was made before removal from the matrix. After 

 removal from the matrix the bones were placed in the mold and cemented together 

 in that position, a position shown to be quite nattiral by the artictdar surfaces. The 

 divarication and curves of the fingers have been given as demanded by the articular 

 surfaces. The elbow, it is seen, is strongly bent, and it seems certain, because of 

 the humeral and epipodial articular surfaces, that this flexure was the usual one in 

 life; complete extension of the forearm would have been impossible. 



Pelvic girdle and extremity: The pelvis of specimen No. 650 was somewhat 

 injured in collection, but enough remains to show its absolute identity in char- 

 acters and size with that of specimen No. 651, of which only the ilium and ischium 

 of the right side are missing. The pelvis is distinctly of the true pelycosaur type, 

 but is especially characterized by the massive sutural union of the pubes. 



The ilium (fig. 32 a, il) agrees quite with that figured by Williston in his American 

 Permian Vertebrates (plate xxxvii, figs. 4, 5) and there tentatively referred to Ophia- 

 codon. It has a long and slender posterior prolongation, in part wanting in the present 



Fig. 32. — Ophiacodon mirus Marsh, X ^• 



A, left pelvic bones, from without. 



B, the pelvis, from above. 

 il, ilium; pu, pubis; is, ischium. 



specimens. In the articulated skeleton the bone 

 lies somewhat obliquely, with the posterior ex- 

 tremity elevated. This posterior process is ver- 

 tical and thin on the posterior part ; anteriorly it 

 has a transverse thin shelf or plate, jutting inward. The articular surfaces for the 

 sacral ribs are at the anterior end of this shelf, partly in front, partly below, forming 

 an oval excavation and showing a strong union with the ribs. The sutural borders 

 for union with the pubis and ischium are strong and massive, meeting a little 

 below the middle of the acetabulimi in rather more than a right angle, that for 

 the ischium a little longer than that for the pubis. On the inner side the convex 

 thickening which joins the posterior end of the pubic symphysial thickening limits 

 the brim of the true pelvis, the false pelvis extending far in advance. 



The pubis (figs. 32 and 34 b) projects strongly forward, with a heavy lateral 

 bar, curved somewhat inwardly. On the margin of these bars, on the outer side at 

 about the middle, there is a thin, everted pectineal process. The two pubes meet 

 in a very thick and strong median symphysis very unlike that of either Dimetrodon 

 or Varanosaurus, where the general shape of the pubis is nearly the same. The two 

 articulated bones extend far in front of the brim of the true pelvis, as a sort of 

 shallowly concave, nearly horizontal trough, supported on its sides by the thick- 

 ened bars. Back of the broad symphysis the two bones together form a concave, 



