402 



TITANOTHERES OF ANCIENT WYOMING, DAKOTA, AND NEBRASKA 



referred the cranium is apparently much less dolicho- 

 cephalic than that of D. hyognathus or D. longiceps. 

 Comparison with Dolichorhinus superior is also diffi- 

 cult and unsatisfactory; in D. superior the premolars 

 appear to be different in contour, also their cingula 

 are not so heavy; the measurements of the superior 

 teeth (p'-m^) in these two species are approximately 



assigned this animal to Palaeosyops. Osborn at first 

 regarded it as belonging to the genus Manieoceras but 

 subsequently recognized the prevailing dolichoce- 

 phalic characters and placed the animal near Dolicho- 

 rhinus. 



Lectotype lower jaws of D. vallidens (Am. Mus. 

 5098). — Comparison with typical lower jaws of D. 



FiGTJKE 340. — Skulls showing progressive dolichocephaly in the Mesatirhinus-DoUchorhinus 



phylum 



Top and palatal views. One-eightli natural size. A, Ai, Mesatirhinas petersoni, British lilus. (formerly Am. Mus. 1556), 

 Big Bone Mountain, Henrys Fork, Bridger Basin, Wyo., Bridger D; B, Bi, Dolichorhinus superior, Field Mus. 12188 

 (type), Uinta Basin, Utah, Uinta B 1; C, Ci, D. Usngiceps, Carnegie Mus. 2347 (type), Uinta Basin, Uinta B 2; D, Di, 

 J), hyognathus, Am. Mus. 1851, White River, Uinta Basin, Uinta B 2. pn^. Primary border of the posterior nares; 

 pn', secondary border of the posterior nares. 



the same — 185 millimeters (estimated) in D. vallidens 

 and 182 in D. superior. The hypocone on m^ prob- 

 ably absent in D. vallidens, is present and strong in D. 

 superior. The upper teeth of D. vallidens (paratype) 

 are structurally ancestral to those of Diplacodon, but 

 so also are the upper teeth of Mesatirhinus petersoni. 

 History. — The species was at first referred by Cope 

 (1885.1, p. 700) to the genus Palaeosyops. Earle also 



hyognathus from both Washakie B 2 and Uinta B 2 

 shows that D. vallidens was a smaller animal and some- 

 what more primitive in the details of the lower pre- 

 molars. (See fig. 353.) 



The chin is only partially preserved and with it the 

 root of the right canine, which is stouter than in sup- 

 posed females of D. hyognathus. The first lower pre- 

 molar, as indicated by the alveolus in Cope's drawing 



