NO. 2127. 



OSTEOLOGY OF THESCELOSAURUS—GILMORE. 



607 



THE PELVIC ARCH. 



The pelvic arch is sufficiently diagnostic of the genus to separate 

 Thescelosaurus at once from all other known dinosaurs. 



The bones to be described below pertain to the type-specimen 

 No. 7757, U.S.N.M. 



Uium. — Both ilia are present, but only the right one is available 

 for study and it lacks a portion of the posterior end, as shown in 

 jBgure 17. The ihum is elongate antero-posteriorly, and very narrow 



Fig. 17.— Pelvis and saceum cf Thescelosaurus neglectus Gilmoee. Type. Cat. No. 7757, 

 U.S.N.M. \ NAT. SIZE. Viewed feom the right side, il, Ilium: is, ischium; p, peepuuis; 

 p', postpubis. The ilium is deawn feom an oblique view. 



vertically. In the latter particular it is relatively narrower even than 

 the ihum of Camptosaurus depressus Gilmore. The preacetabular 

 process is long and tapering, triangular in cross-section near its middle, 

 but flattened toward the tip, which terminates anteriorly in a sharp- 

 pointed end. 



The missing posterior portion as restored in outline in figure 17, 

 also plate 80, is after the ilium of Camptosaurus. On the inner side 

 behind the acetabulum a comparatively thin but wide shelf of bone 

 (fig. 17) is given off at right angles to the main portion of the ihum 

 and extends inward, articulating by suture along its inner margin 

 with the ribs of the two posterior sacral vertebrae, 



