370 



TITANOTHERES OF ANCIENT WYOMING, DAKOTA, AND NEBRASKA 



The peculiarities of the jaw of M. manteoceras (fig. 

 310, PI. LI) are as follows: 



1. In most of the jaws there is a narrow postcanine 

 diastema (18 mm. in No. 1566). 



3. The powerfully rooted canines involve a sharp 

 convexity of the bone opposite the alveoli, followed by 

 a sharp depression in the outer face just below the 

 postcanine diastema. 



4. The chin, as seen from below, is 

 broad and gently convex anteroposte- 

 riorly and transversely, but on account of 

 the great variation in both species it is 

 difficult to express exactly the differ- 

 ences in the horizontal rami between 

 Manteoceras manteoceras and Mesati- 

 rhinus petersoni. 



5. The principal constant difference 

 is the weaker chin of Mesatirhinus, in 

 old jaws of which the lower border of 

 the ramus is straighter than in Manteo- 

 ceras; the ramus also seems stouter and 

 deeper and rapidly increases in depth 

 posteriorly from 54 millimeters behind 

 Pa to 64 behind m2 and 87 behind ma. 



6. In adult jaws the coronoid is of an 

 entirely different shape from that of 

 Palaeosyops, being elevated and broad 

 at the top with the summit gently 

 recurved, whereas in Palaeosyops it is 

 pointed and well recurved at the top. 

 It resembles that of Mesatirhinus but 

 lacks the posterosuperior prolongation, 

 and the superior portion of the process 

 is flattened anteriorly with sharply 

 angulate anterior external and internal 

 borders. 



7. The angle is produced decidedly 

 downward and backward, and there is 

 a rugose outer border in the old males. 



8. The posterior border of the jaw 

 between the angle and the condyle is 

 somewhat incurved in some specimens 

 but nearly straight in others. 



Measurements of lower jaws of Manteoceras 

 manteoceras, in millimeters 



Figure 310. — Lower jaw of Manteoceras 

 One-fourth natural size. A, M. manteoceras, Am. Mus. 1566, Bridger Basin, Wyo. level probably C or D. 

 B, M. manteoceras, Am. Mus. 1563, Bridger Basin, level probably D; very progressive lower jaw (front 

 part corrected from No. 1560). C, M. uintensist. Am. Mus. 2033 (reversed), White Elver, Uinta Basin, 

 Utah, Uinta C; doubtfully referred lower jaw. 



Pi-mj 



Pi-P4 



Mi-m3 



Condyle to incisive 

 border 



Condyle to bottom of 

 angle 



Depth of ramus below 

 m3 



Length of symphysis- 



Am. Mus. 



1566; Bridger 



C orD 



182 



73 



110 



360 



165 



86 

 109 



Am. Mus. 

 2353; Washa- 

 kie A 



195 



76 



117 



96 



2. The opposite incisor series are placed more trans- 

 versely than in the premaxillaries above, in which 

 they are more convergent. 



Detailed cTiaracters. — Probably as a sex- 

 ual character the skull itself is not so large as that of the 

 largest Bridger specimens, the estimated basilar length 

 (490 mm.) being less than in the large male M. manteo- 



