524 TITANOTHEKES OF ANCIENT WYOMING, DAKOTA, AND NEBRASKA 



Measurements of sTcuUs and jaws associated with and referred to the Menodus phylum, in millimeters 



» Estimated. 



Menodus heloceras (Cope) 



{Megaceratops helocerus Cope, 1873; "Titanotherium helocerus" 

 Osborn, 1902) 



Plates XLVII, C XXIII, CXXIV; text figures 168, 378, 399, 

 409, 435, 436, 613, 639 



[For original description and type references see p. 212. For skeletal characters see 

 p. 681] 



Type locality and geologic horizon. — Cedar Creek, 

 Logan County, Colo.; lower Titanotherium zone. 



Specific characters. — Skull small, premaxillaries to 

 condyles estimated about 603 millimeters, tip of 

 nasals to top of occiput about 545. Dolichocephalic 

 (index unknown), width across zygomata 392-425 

 millimeters. Horns small, "elevation 50 millimeters" 

 (Cope), basal section trihedral (with flattened, subequal 

 external, internal, and posterior faces), tip rounded. 

 Horns above antorbital malar ridge. Nasals squared 

 distally, free length and breadth equal (100 by 100 

 mm. fide Cope). Buccal swelling of zygoma incipient. 

 Premolar-molar series 265 milhmeters (estimated). 



Materials. — The type skull was found on Cedar 

 Creek, Logan County, Colo., the same geographic 

 region which yielded the various Symborodon skulls. 

 The characters based upon the very imperfect type 

 skull (Am. Mus. 6360) are supplemented by those of 

 the much more perfectly preserved skull (Am. Mus, 

 14576) found in Wyoming; the latter is in a very 

 primitive stage of development (fig. 436), especially 

 in regard to the small size of the molars, m'-m^, 

 which measure 170 millimeters. 



' Eight side . ■< Left side. 



Description of the type. — This is the smallest and 

 apparently also the most primitive member of the 

 Menodus phylum; it approaches even the Eocene 

 titanotheres in its slender, narrow occiput (Pis. 

 CXXIII, CXXIV) and its slender zygomata. In 

 lateral view we note the weU-marked postorbital 

 processes of the frontals and the open condition of the 

 auditory meatus. All these characters point toward 

 affinity with Menodus. The specimen, as indicated 

 in Plate CXXIV, A\ is in fragmentary condition, 

 the facial region being largely wanting. The nasals 

 have been lost, but as measured by Cope they were 

 equal in length and breadth (100 by 100 mm.), a point 

 of significance in the consideration of the affinities of 

 thi.s animal because in M. trigonoceras and in the type 

 of M. giganteus the breadth also equals the length, 

 whereas in all stages of Brontops the breadth exceeds 

 the length. Cope's other measurements are as 



follows : 



Measurements of Menodus heloceras 



Millimeters 



Least width of paiietal plane 104 



Elevation of horn core 50 



Length of free nasal bones 100 



Width of free nasal bones at base 100 



The rudimentary condition of the horns also indi- 

 cates that this animal belongs in the lower Titano- 

 therium zone. The horn section (figs. 399, 435) con- 

 sists of the relatively acute anterior angle, an external 

 angle, and a gently rounded internal angle, the last 

 attributable to the absence of any connectmg crest 



