24 



PROCEEDINGS OF THE NATIONAL MUSEUM 



VOL. 77 



Pubis. — The small bone illustrated in Figure 16 is regarded as the 

 right pubis. It is a remarkably small bone for so large an animal, 

 the whole prepubic portion measuring only 140 millimeters in length, 

 less than one-half the length of the Stegopelta pubis.^^ The anterior 

 portion is a thin vertical blade of bone terminated anteriorly by a 

 slightly thickened rugose end that is rounded off from above down- 

 ward. On the internal surface at about its mid length the postpubis 

 branches off, continuing backward and downward. The postpubic 

 branch terminates in a vertically expanded end that in this specimen 

 is perfectly preserved (fig. 16). On the outer side much of the 

 surface has been eaten away, leaving one at a loss to understand where 



and how this bone artic- 

 ulated with the ilium, as 

 there is no indication of 

 an enlarged articular 

 area. 



The small size of the 

 pubis in these Upper 

 Cretaceous armored di- 

 nosaurs has been indi- 

 cated by Nopcsa in Sco- 

 JosaurtLS, but it was so 

 poorly preserved that he 

 could not determine its 

 shape. Ankylosaurus also has a very much reduced pubis ^- appar- 

 ently coossified to the ischium and Nopcsa remarks that "it neither 

 seems very large in Polacanthusy The outer surface is much 

 roughened. 



Ischia. — Both ischia are present, the left one being complete, the 

 right lacking its distal fourth. The ischium is a moderately long 

 curved bone having a widely expanded proximal and a bluntly 

 pointed distal extremity. On the outer surface the proximal end is 

 concave fore and aft and forms a part of the acetabulum. The 

 acetabular margin is unusually straight. Below this end the shaft is 

 flattened transversely and gradually decreases in width toward the 

 distal end, the taper becoming more pronounced a little below the 

 mid-length where the bone also bends downward, as shown in Figure 

 17. A flat roughened area on the external surface at this bend in- 

 dicates the point of attachment of an important ligament. On the 

 inner side the surface of the bone gives no indication that it was 

 in contact on the midline with its fellow of the opposite side though 

 doubtless there was a cartilaginous union of the two. 



Figure 16. — Right pubis of Palaeoscincus rugosi- 

 DENS. Type. No. 11868, U.S.N.M. Lateral view. 

 A., Anterior end ; p.. Posterior end ; Pp., Post- 

 pubis. One-third natural size 



^ Moodie, R. L., Kans. Univ. Sci. Bull., vol. 5, No. 14, 1910, p. 265, pi. 58, fig. 1. 

 =2 Romer, A. S., Acta Zoologiea, vol. 8, 1927, fig. 8. p. 243. 



