PERMIAN VERTEBRATES 719 



ectepicondylar notch. Length .038 111 , width proximal end .oio5 m , distal end 

 .0205 111 . Plate III, Fig. 8, a, b, c, d. [No. 6545.] 



UlncE. — There are two types of ulna distinguished by the size only. One 

 is nearly as large as the ulna of Dimetrodon incisivus and quite similar 

 to it ; the proximal end only is preserved ; the other is Smaller, represented 

 by the proximal end also, and probably belongs to one of the smaller 

 species of Clepsydrops. Plate III, Fig. 9. [Nos. 6546 and 6547.] 



Femora. — The femora are mostly of the same type, but show considerable 

 variation in size. They all have the distal articular surfaces upon the inner or 

 lower face of the distal end, showing that the leg was habitually flexed and the 

 animal progressed, probably, with the belly on or near the ground, in the 

 manner of the alligator. One of the medium sized forms is figured (No. 

 6548). Length of one specimen, .077™; a larger specimen, .107™. Plate IV, 

 Fig. 1, a and b. [Nos. 6548, 6549, 6550, 6551, 6552, and 6553.] 



The distal ends of two very small femora are present ; they lack well- 

 developed articular surfaces, though the contour of the extremity is the same 

 as in the larger specimens. It seems probable that they are immature forms. 

 [No. 6552.] 



Tibia. — There is one complete tibia, somewhat crushed, and the proximal 

 end of another. The whole bone is larger at the proximal than at the distal 

 extremity, and is considerably curved. The shaft is more or less flattened. 

 The proximal end has two faces, which are distinct, or nearly so ;_ they are 

 oblong and lie with their long axes nearly at right angles to each other. The 

 anterior extremity of one anticular face forms the upper portion of the cne- 

 mial crest. Measurements: length, .o49 m . Plate IV, Fig. 2, a and b. [No. 

 6555-] 



Fibula. — What appears to be a fibula is .05 3 m long. It is a slender bone, 

 expanded at the extremities and quite strongly curved. Plate IV, Fig. 3. 

 [No. 6554.] 



Ilia. — There are two types of ilia of about the same size. Each presents 

 two articular faces at the distal portion for articulation with the ischium and 

 pubis and a rather deeper articular portion of the acetabulum ; at the upper 

 portion of the acetabulum there is a prominent overhanging process. The 

 two forms differ principally in the anterior process of the ilium with which it 

 is attached to the sacral vertebrae. In one form it extends almost straight 

 forward (No. 6556) and in the other (No. 6557) it is curved and the anterior 

 end is somewhat lower than the posterior. The inner side of each presents 

 strong longitudinal ridges and there does not seem to be any articular facet 

 for the vertebrae. In an incomplete fragment, in which the ischium and 

 ilium are in contact, the acetabulum is seen to be quite deep. Plate IV, 

 Figs. 4 and 5. [Nos. 6556, 6557, and 6558.] 



