68 



BULLETIN 110, UNITED STATES NATIONAL MUSEUM. 



The ischia in Antrodemus as compared with the pubes are slender. Proximally 

 they are expanded, forming a Y-shaped extremity having two distinct articulating 

 processes (fig. 1, pi. 12), the posterior one articulates with the ischiac peduncle of 

 the ilium, the anterior one with a posterior extension of the pubis, the superior 

 concave surface between forming the ischiac contribution to the inferior boundary 

 of the acetabulum. Below this head the bone rapidly contracts on the anterior and 

 posterior borders more especially the latter, but again is widened by the develop- 

 ment on the antero-internal side of a wide obturator process (ob. pr. fig. 3, pi. 12). 

 A slight notch marks the distal extension of this process; a sharp ridge passes 

 obliquely downward from this notch to the center of the inner surface of the shaft, 

 where it gradually merges into the shaft below the middle of the bone shown in 

 figure 4, plate 12. The distal end is slightly expanded antero-posteriorly, with a 

 broadly convex rugose distal end. The inner side of the distal half of the ischium 

 is flattened; the outer rounded throughout nearly the entire length of the shaft. 



Where articulated the ischia are in contact along the median line from the 

 proximal border of the obturator process to the distal end, except for a very small 

 aperture formed by the notches on the side of the obturator process, as is shown in 

 figure 1, plate 12. This median union of the ischia and pubes renders the pelvic 

 opening very small when the large size of the animal is taken into consideration. 

 The greatest transverse width of this opening in specimen No. 8367, U.S.N.M., a 

 very large individual, is only 140 mm. wide. All aspects of the ischia are well 

 illustrated in plate 12, which was drawn, under the direction of Prof. O. C. Marsh, 

 from specimens in the Yale University Museum. They agree closely in every 

 particular with the ischia of Antrodemus vdlens in the United States National Mu- 

 seum collections. 



Measurements of ischia of Antrodemus valens Leidy. 



Length of ischium from middle of acetabular border to distal, end 



Greatest diameter of proximal end 



Greatest diameter of distal ends '. 



Least diameter of shaft 



No. 8367, 



No. 4734, 



U.S.N.M. 



U.S.N.M. 



mm. 



mm. 



650 



575 



225 e 



260 



135 



115+ 



38 



35 



No. 2323, 

 U.S.N.M. 



490 



177 



93 



27 



c=estimated. 



HIND LIMB AND FOOT. 



Femur (/.). — The femur of Antrodemus is longer than the tibia, with a curved 

 shaft, the arctuation being forward (fig. 1 and 4, pi. 14). Although somewhat 

 larger than that of Ceratosaurus they closely resemble one another in form and in 

 the position of the areas for muscular attachment. Both femora are present in 

 specimen No. 4734, U.S.N.M., as shown in plate 13, and both are in an excellent 

 state of preservation. The bone is remarkably light for its size. The middle portion 

 of the shaft is angularly rounded in cross section with a hollow marrow cavity (fig. 6, 

 pi. 14). The articular head is clearly defined, and when articulated extends well 

 within the acetabulum. The fourth trochanter is an elongate ridge on the posterior 

 internal side and entirely upon the proximal half of the shaft. This trochanter in 



