DISCOVERY OF THE TITANOTHERES AND ORIGINAL DESCRIPTIONS 



223 



6, 1889 (Marsh, 1889.1); skeleton and restoration, this 

 monograph. Plates XCVI-CIII, CXCV-CCXXIX. 



Type locality and geologic horizon. — "Near the 

 White River in northern Nebraska. " "The geological 

 horizon is in the upper part of the Brontotheriwn 

 beds [Chadron formation, Titanotherium zone] " 

 (Marsh). "Upper levels of middle beds at least 60 

 feet below the top of the upper beds" (Hatcher, 1901). 



Figure 180. — Type (holotype) lower jaw of Brontops dispar 

 Nat. Mas. 4941. After Marsh, 1887. One-eighth natural size. 



Type. — A skull and skeleton, Yale Mus. 12048. 

 (See fig. 179.) 



Specific characters. — Marsh did not formally sepa- 

 rate the specific from the generic characters. He 

 records the fact that the skull is large and massive, 

 with widely expanding zygomatic arches and stout, 

 robust horn cores, projecting well forward. 



Etymology. — roiustus, robust (that is, strong as an 

 oak, rohur). 



Present determination. — The genus and species are 

 valid. The species is described also on pages 492-499. 



Brontops dispar Marsh, 1887 



Cf. Brontops dispar, this monograph, page 488 



Original reference. — Am. Jour. Sci., 3d ser., vol. 34, 

 pp. 327, 329, figs. 7, 8 (jaw); not figs. 5, 6 (skull), 

 October, 1887 (Marsh, 1887.1). 



Type locality and geologic horizon. — Found on Hat 

 Creek, Sioux County, Nebr., by J. B. Hatcher, May 

 14, 1886; Chadron formation {Titanotherium zone), 

 middle level. 



Type. — "A nearly complete skull with lower jaws 

 and entire dentition." (Marsh.) Nat. Mus. 4941 

 (skull D). (See fig. 180.) 



Characters. — Marsh writes: "The skull is less mas- 

 sive and proportionately more elongate than in the 

 type species, and the lower jaw more slender." In 

 the same brief passage Marsh described a young skull 

 (Nat. Mus. 4258) as belonging to the same species; 

 this is a somewhat more primitive type (Brontops 



brachycephalus) belonging to a younger individual 

 (p. 483). 



Etymology. — dispar, uneven, probably in allusion to 

 the asymmetrical distortion of the type skull. 



Present determination. — The species is valid and is 

 now referred to Brontops. 



Menops Marsh, 1887 

 Cf. Menodus, this monograph, page 522 



Original reference. — Am. Jour. Sci., 3d ser., vol. 34, 

 p. 328, October, 1887 (Marsh, 1887.1). 



Type species. — Menops varians. (See below.) 

 Generic characters. — Marsh writes: 



The present genus is most nearly related to Diconodon and 

 in its molar teeth agrees with that form. It differs in the 

 presence of two upper incisors on each side. The superior 

 dentition is as follows: Incisors, 2; canine, 1; premolars, 4; 

 molars, 3. 



Etymology. — Menodus; &\p,i ace; resembling Menodus 

 (cf. Brontops, above). 



Present determination. — The incisors are vestigial, 

 the alveoli being very small. The skull presents re- 

 semblance to both Menodus and Allops. The generic 

 reference is to Menodus. 



Menops varians Marsh, 1887 



Cf. Menodus varians, this monograph, page 535 



Original reference. — Am. Jour. Sci., 3d ser., vol. 34, 

 p. 328, fig. 9, October, 1887 (Marsh, 1887.1). 



Type locality and geologic horizon. — " Brontotherium 

 beds of Dakota" (Chadron formation, Titanotherium 

 zone); exact locality and level not stated. George 

 A. Clarke, collector. 



FiGUKE 181. — Type (holotype) skull of Menops varians 

 Yale Mus. 120G0. Front view. One-eighth natural size. 



Type. — A well-preserved skull (Yale Mus. 12060). 

 (See fig. 181.) 



Specific characters.— Not separated by Marsh from 

 generic characters. (See above.) 



Etymology. — varians, variant; allusion doubtful, but 

 possibly to the somewhat aberrant character of the 

 type skull. 



Present determination. — The species is valid and is 

 referred to Menodus. 



