532 



TITANOTHERES OF ANCIENT WYOMING, DAKOTA, AND NEBRASKA 



From Allops crassicornis we observe that M. gigan- 

 teus is distinguished by the greater length of p'-m^ 

 and especially of the true molars {M. giganteus 246-285 

 mm., A. crassicornis 220), by the greater length of the 

 nasals, and by the much lower zygomatic index. 



Figure 442. — Skull of Menodus giganteus 



Yale Mus. 12010, type of Broniotherium ingens Marsh. Front view. 

 One-eighth natural size. This view shows well certain features 

 of Menodus, as follows: Horns trihedral and pointed, nasals dis- 

 tally broad, zygomata deep with small buccal expansions, canines 

 large, cheek teeth with sharp external cingula. 



From Brontops robustus M. giganteus is readily 

 distinguished as follows: 



Measurements of Menodus giganteus and Brontops robustus, in 

 millimeters 



Geologic and geographic distribution. — The geologic 

 range of this species as recorded by Hatcher is from 

 the summit of B, the middle zone, to the summit of C, 

 the upper Titanotherium zone. 



Materials. — The species is represented by Pomel's 

 type jaw, which has been destroyed and is known 

 only from Leidy's figure and measurements; also 

 by Marsh's excellent type skull of "B. ingens" in the 

 Yale Museum (No. 12010), found in Colorado; by 

 three skulls in the American Museum (Nos. 505, c? ; 

 1066, c? ; 1067, ? ); by six fine skulls in the National 

 Museum (No. 1220, etc.) ; and by the superb skull asso- 

 ciated with cervical and anterior dorsal vertebrae 

 (Pis. CXXXIX, CXL) in the Field Museum of Chicago 

 (No. P 5927). The largest skull of all is that in the 

 University of Wyoming Museum. 



According to the measurements given in the table 

 above, the skulls Am. Mus. 1066 and 1067 and Nat. 



Mus. 4291, which are all referred here to M. gigan- 

 teus, are much closer to M. trigonoceras and are sepa- 

 rated from the true M. giganteus skulls by a consider- 

 able gap. 



Characters of Marsh's type of "B. ingens." — The 

 principal characters of the type skull as given by 

 Marsh with measurements are entered in the table 

 above. Additional characters are as follows: This 

 animal is in the eighth stage of growth, advancing 

 toward the ninth. The tips of the internal cusps of 

 m'^ are slightly worn, barely showing the dentine. 

 The top of the skull is uncrushed but somewhat 

 depressed just behind the connecting horn crest. 

 The right horn and right half of the nasals are partly 

 restored, although figured as complete in Plates 

 CXXXVII and CXXXVIII. In the left horn, which 

 is more perfect, the triangular shape is very marked. 



Figure 443. — SkuU of Menodus giganteus 



Yale Mus. 12010, type of Broniotherium ingens Marsh. Palatal view. 

 One-eighth natural size. Drawing made by Berger under the 

 direction of Marsh. This view shows Menodus characters as 

 follows: Skull dolichocephalic, nasals long and distally broad or 

 squarish, horns trihedral in section and pointed, tooth rows rec- 

 tilinear, cheek teeth with sharp internal and external cingula, 

 premolars with large postero-lnternal cusps, molars elongate an- 

 teroposteriorly, zygomatic expansion moderate. 



The anterior angle of the horn runs directly into the 

 nasals. The premolars exhibit very broad internal 

 cingula and pronounced external cingula; the first 

 premolar displays an internal crest formed of the 

 deuterocone and tetartocone. The second and third 

 premolars have the tetartocones more distinct, ele- 

 vated, and sharply separated off from the cingula; 

 the deuterocones and tetartocones are subequal, 



