530 



TITANOTHERES OF ANCIENT WYOMING, DAKOTA, AND NEBRASKA 



medifossette of the rhinoceros and horse molar. Just 

 internal to this pit two ridges enter the median valley. 

 These are apparently homologous with the "crochet" 

 and " antecrochet " of the rhinoceros and horse molars. 

 The molar teeth also exhibit well-developed external 

 cingula; the internal cingula, as in all other titano- 

 theres, are incomplete opposite the protocones. 



Skulls of M. trigonoceras. — Of the six skulls in the 

 National Museum collection referred to Menodus 



Figure 440. — Skull of Menodus trigonoceras 



In the Colorado Museum, Denver. The nasals and horns were detached when 

 the skull was found, but there is no question as to the association. 



trigonoceras one (Nat. Mus. 4257) is recorded from the 

 upper levels of the middle Titanotherium zone. It 

 belongs to a small male in the seventh stage of growth. 

 The anterior measurement of the canines is 42 milli- 

 meters (estimated). Two extremely small vestigial 

 incisors persist upon one premaxUla only. In the 

 first superior premolar the tetartocone is connected 

 by a confluent crest with the deuterocone, as in other 

 species of this genus. The tetartocone cusp on p^, 

 p^ is very distinct, especially in p''. 



From the vertex to the tips of the nasals the skull 

 measures 665 millimeters; the free length and the free 

 width of the nasals are nearly equal, namely, 120 by 

 125 millimeters. The horns measure 150 millimeters 

 from the edge of the anterior nares to the tips. On the 

 inferior surface of the skull the vomer extends back 

 from the presphenoid as a distinct narrow keel. 



In another skull, an old male (Nat. Mus. 1219), as in 

 the more advanced or eighth stage of growth, the horns 

 measure 195 millimeters as compared with 150 in the 

 specimen just described. This is a natural growth 

 increase. It is important to note that the nasals are 

 practically the same length as in the younger speci- 

 mens, namely, 115 millimeters; but they are greatly 

 increased in breadth (160 mm.), also in the rugose 

 expansion of their tips, which support a pair of 

 lateral tuberosities. This animal is evidently a very 

 old male, and its senescent character is emphasized by 

 the entire disappearance of the vestigial upper incisors. 

 It is also a very large individual. The premolar-molar 

 series measures 345 millimeters. 



In contrast with the two skulls described above 

 there is a third skull (Nat. Mus. 4701) belonging to 

 a young female which is recorded by Hatcher from 

 level C 1 of the upper Titanotherium zone. The 

 premolar-molar series measures 300 millimeters. The 

 female sex is indicated by the small, pointed ca- 

 nines (34 mm.). Inconsistently with its high geo- 

 logic level as recorded, the skull exhibits a relatively 

 low stage of development in its premolar teeth, the 

 tetartocones being less clearly separated off than in the 

 old male above described. Although the animal is still 

 young, the incisors have entirely disappeared, as well 

 as all traces of their alveoli. The internal cingulum 

 of the premolars is quite as prominent in this female 

 as in the males, again proving that the cingulum is 

 not a sexual character. There is a large hypocone on 

 the last superior molar, which thus appears to be a 

 specific if not a generic character. 



The Ottawa Museum skull jrom the lower Oligocene 

 of Swift Current River, Assinihoia, Canada. — The frag- 

 mentary cranium described and figured by Cope 

 (1891.2, p. 10, pi. 6) as "Menodus americanus" very 

 probably belongs to M. trigonoceras. 



Menodus giganteus Pomel 



(" Brontotherium" ingens Marsh, 1873; "Titanotherium ingens" 

 Osborn, 1902) 



Plates XVIII, XX, XXIV, XLVII, XLIX, CXXXIII, 

 CXXXV-CXLI; text figures 24, 159, 227, 228, 375, 381, 

 387-389, 391, 393, 394, 396, 399, 400, 406, 409, 441-446, 617- 

 619, 630, 640, 642, 701, 713, 715-719, 744 



[For original description and type references see p. 204. For skeletal characters 

 see p. 687] 



Geologic horizon. — Upper Titanotherium zone. 



Specific characters. — Skull very large, premaxillaries 

 to condyles 770-825 millimeters, tip of nasals to top 

 of occiput 712-755+ . Dolichocephalic, width across 



