564 



TITANOTHERES OF ANCIENT WYOMING, DAKOTA, AND NEBRASKA 



is much deeper than in the type of B. Jiatcheri. This 

 specimen of B. Jiatcheri, moreover, tends to bridge over 



Figure 466. — Skull of Brontotherium hatcheri 



followed by a depression; (8) in the gentle slope of the 

 occipital vertex in side view; (9) in the characters of 

 the cheek teeth, which have very 

 large circular tetartocones set well in 

 toward the middle of the crown, 

 vestigial external cingula, and low, 

 rounded internal cingula and 

 rounded external faces; (10) in the 

 minute p'. In general this skull also 

 supports the specific separation of B. 

 hatcheri as a lower stage of B. gigas. 

 Comparative measurements are given 

 above. 



University of Wyoming skull of B. 

 hatcheri. — A skull (figs. 466, 467) and 

 associated jaw (fig. 468, A) which are 

 provisionally referred to this species 

 are in the University of Wyoming. 

 They were discovered by Mr. W. H. 

 Reed in the upper Titanotherium zone 

 in the northeastern corner of Carbon 

 County, Wyo. The absence of a con- 

 necting crest, the subcylindrical form 

 of the horns, and the form of the nasals 

 at first suggest the type of Megacerops 

 coloradensis ; but the skull differs in 

 many points from that of Megacerops 

 acer, and the measurements are on the 

 whole closer to those of B. hatcheri. 

 The fourth upper premolar measures 

 41 by 52 millimeters (ap. by tr.); the 

 lower jaw from front of canine to back 



Univ. Wyoming Mus. 1; Chadron C (flde W. H. Eeed); northeast corner of Carbon County.Wyo. Side of an^lc 598' Other measurements are 

 ¥iew. One-sixth natural size. The horns and measurements are close to those of S. hatcheri, the basal • ^ u ' 



section of the horns recalls B. tichoceras, and the associated lower jaw is characteristic of Bronlotherium. glVen aDOVe. 



the gap between B. leidyi and B. gigas, because while 

 approaching the latter in the connecting crest between 

 the horns and in its larger size, it resembles the older 

 form of B. leidyi in the following respects: (1) The 

 canines, incisors, and grinding teeth are similar, (2) 

 the horns are intermediate in position between those 

 in B. leidyi and B. gigas, (3) the top view of the skull 

 is similar to B. leidyi. 



Field Museum sTcull of B. hatcheri. — In the Field 

 Museum, Chicago, there is a beautiful and nearly 

 uncrushed skull of this species from Phinney Springs, 

 S. Dak., recorded from the middle zone, at a level 75 

 to 100 feet above the Pierre shale. The skull is a 

 typical Brontotherium in every respect and contrasts 

 sharply with the Brontops-Allops- Menodus group 

 while agreeing with Megacerops and Brontotherium, 

 especially (1) in the shape of the nasals, which are 

 gently tapering and distally decurved in both top and 

 side views; (2) in the anterior narial opening as seen in 

 side view; (3) in the upward flexm-e anteriorly of the 

 tooth rows; (4) in the very narrow, rounded bridge 

 over the infraorbital foramen; (5) in the relatively 

 small orbit; (6) in the shape of the connecting crest 

 and horns; (7) in the midparietal convexity, which is 



Figure 467. — Skull of Brontotherium hatcheri 



Univ. Wyoming Mus. 1. Front view. One-sixth natural size. This view 

 shows well the resemblances to B. hatcheri. (Compare Pis. CLXVII, 

 CLXIX, A2, CLXX, B.) The specimen is much crushed and distorted. 



Additional observations on B. hatcheri. — This form is 

 not very clearly separated from B. gigas, since it was 



