84 AMERICAN PERMIAN VERTEBRATES 



ectepicondylar process is much more prominent and transverse 

 in position. The concavity of the radial side is much deeper. 

 With the humerus of D. incisivus the resemblance is somewhat 

 greater. It also resembles the humerus from New Mexico assigned 

 by Case to Dimetrodon navajoicus, but I feel assured the forms 

 are of different genera. Because of its size and general characters 

 the present specimen may well belong with Sphenacodon, rather 

 than Ophiacodon. 



Ulna (Plate XXXV, Fig. 9).- — The ulna is a distinctly less 

 slender bone than that of Dimetrodon; its olecranon process is 

 not produced in the specimen figured, and scarcely so in other 

 fragmentary specimens. The sigmoid fossa is not as deep, and 

 the shaft is broader. 



Radius (Plate XXXV, Figs. 10, 11). — The radius also is less 

 slender than in Dimetrodon. The bone is moderately expanded at 

 either extremity, with the concavities of the sides nearly equal. 

 The upper, articular end is nearly semicircular in outline; the 

 lower one, subcrescentric, with the outer horn the thinner. 



POSTERIOR GIRDLE AND EXTREMITY 



Ilium (Plate XXXVII, Figs. 4, 5). — ^Among all the bones of the 

 posterior girdle and extremity there is none so characteristic as 

 the ilium. The present ihum differs materially from that of 

 Dimetrodon, resembling more that of Theropleura or Varanosaurus 

 in its narrow posterior prolongation and the presence on the 

 inner side of the strong, horizontal, keel-like projection, quite as 

 Case has figured it in Theropleura. The articular surface for the 

 ischium is much longer than that for the pubis, and the two meet 

 in nearly a right angle. Of the five or six ilia in the collection, 

 the one figured is the smallest. 



Ischium. — The ischia, of which there are several in the collection, 

 all incomplete, agree quite with those of Theropleura, as figured 

 by Case (Pelycosauria, Plate III, Fig. 6). The ischia generally 

 in the Permian reptiles are uncharacteristic. 



Pubis. — The pubes seem to be quite similar to those of Varano- 

 saurus, having a strongly projecting anterior plate, twisted to a 

 horizontal position in the articulated skeleton. This bone, as 



