132 



BULLETIN 110, UNITED STATES NATIONAL MUSEUM. 



[Amer. Journ. Sci., 1884, vol. 27, p. 329]. The present pelvis resembles that of Ceratosaurus in its 

 general features, but there is no foramen in the pubis. 



There are five vertebrae in the sacrum, firmly coossified with each other, as are also the sacral 

 spines. The sacral vertebrae are grooved below, with the sides of the centra excavated. The caudals 

 have the diplosphenal articulation, and the first caudal bears a chevron. All the bones preserved 

 are very delicate, and some of them, at least, are apparently pneumatic. 



The sacrum measures 15 inches in length, and the 12 caudals following occupy a space of 31 inches. 

 The known remains indicate a reptile about 8 or 10 feet in length. 



The known remains of all the above species are from the Ceratops Beds [Lance formation] of 

 Wyoming. 



The above description by Marsh constitutes practically all that has been 

 written l regarding this species, and the type specimen is here figured for the first 

 time. That Omiihomimus sedens Marsh is closely related to OrnitJiomimus altus 

 Lambe recently described by Osborn 2 is at once apparent upon the most casual 



Fig. 67.— Sacrum of Ornithomimus sedens Marsh. Ventral view. Type No. 4736, U.S.N.M. J nat. size, ac, 

 acetabulum; II, ilium; Is, coalesced ischia, shown in outline; I.p, ischiac peduncle of the ilium; 0, open- 

 ing between coossified ischia; P, pubis; P.p., pubic peduncle of the ilium; Si, S 2 , S3, S<, sacral vertebrae 1 to 4. 



comparison, and, as I have attempted to show, good reasons for their generic 

 separation does not exist at this time. 



The sacrum of Omiihomimus sedens is unusually well preserved and is worthy 

 of a detailed description, especially since this portion of the beautiful skeleton 

 described by Osborn (pi. 35, fig. 2) is somewhat imperfect. 



Sacrum. — The sacral region in Omiihomimus sedens consists of five coossified 

 vertebrae, but of these only four are preserved; the presence of a fifth is clearly 

 indicated by the roughly rugose articular end of the most anterior vertebra for 

 close union with the vertebra which preceded it. In position this missing vertebra 

 corresponds to dorsal 13 in the Struihiomimus skeleton as described and figured 

 by Osborn in the paper cited above. Thus in Omiihomimus sedens and in OrnitJi- 

 omimus altus it would appear that only four vertebrae functioned as sacrals. 



1 A terminal phalanx of the fore foot of this species was figured by Marsh (see figs. 49 to 52, p. 265, Dinosaurs of North America) 

 but the basis of the identification is unknown to me. 



2 Bull. Amer. Mus. Nat. Hist., vol. 35, pp. 738-761, 1917. 



