258 



PROCEEDINGS OF THE NATIONAL MU8EU3I. 



VOL. XXXVI. 



expanded hammer-like end (see la, fig. 31). The distal ends appear 

 to have been in contact as well as the borders of the lower half of their 

 shafts. In C. hrowni this bone is lightly constructed, in this respect 

 approaching the ischia of C. medius. The proximal end has a widely 

 expanded Y-shaped extremity with two distinct articular faces (see is, 

 Plate 16), the one for the posterior peduncle of the ilium being the 

 heavier. Its articular surface is rugose and deeply cupped. The 

 articular surface for contact with the pubis is borne on a thin, quad- 

 rilateral plate which extends down- 

 ward and forward from the main 

 shaft of the bone, and its upper antero- 

 l^osterior concave border completes the 

 acetabular boundary. The straight, 

 truncated end of this plate is flat and 

 thickened transversely, and when in 

 position abuts against an opposing 

 articular face on the posterior end of 

 the pubis at about the middle line of 

 the acetabulum. The lower anterior 

 border is also thickened and is in con- 

 tact with a depressed articular sur- 

 face on top of the postpubis, just pos- 

 terior to the pubic foramen. Behind, 

 the expanded head contracts rapidly, 

 but again widens on the inferior border 

 into a thin, lip-like, downturned, ob- 

 turator process, against which the rod- 

 like shaft of the postpubis rests (see 

 Plate IG). Below this process the 

 shaft contracts and continues as a 

 curved, rod-like shaft to the distal ex- 

 tremity. The position of the obtura- 

 tor process, well up toward the articu- 

 lar end, at once distinguishes the ischium of Cawptosaurns from 

 Hyosilophodon foxii, which has this process about midway between 

 the two ends. 



Fig. 31. — IsniiA m- (".\mptosaurus 



MEDIUS MaKSH. SlPERIOR VIEW. 



Yale Museum ; | nat. size. U, 

 iliac surface ; 1(1, distal ends of 

 SAME. After Marsh. 



Mcasurrmrnlft of Specimen, Cat. No. Ji282, U.S.N.M. 



mm. 

 Greatest length of left iscliium 545 



Greatest width of proximal eud 194 



Greatest width of distal end ''^ 



The pubis. — The description to follow is based on the pubis of 

 C. dispar, No. 1878, Yale Museum, the postpubis from C. medius, No. 

 1880, Yale Museum (see p' , Plate 16). 



As shown in fig. 32, the pubis in Camptosaurus is composed of a 

 flattened prepubic element and an elongated, curved, slender post- 



