222 



TITANOTHERES OF ANCIENT WYOMING, DAKOTA, AND NEBRASKA 



is concave; they are greatly flattened anteroposteriorly, with 

 a ridgelilie outer margin, and connected by a well-raised median 



Figure 178. — Type (holotype) horns of 

 Menodus platyceras 



In the collection of the ]Museum of Comparative 

 Zoology, Harvard University. After Scott and 

 Osborn, 1887. Greatly reduced. A, Front view; B, 

 cross section: C, side view. 



ridge. The posterior face is nearly plane, the anterior is con- 

 vex, so that the section of the horn is plano-convex from base 



SPECIES DESCRIBED BY MARSH IN 1887 



Brontops Marsh, 1887 



Cf. Brontops, this monograph, page 482 



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

 p. 326, October, 1887 (Marsh, 1887.1). 



Type species. — Brontops rohustus Marsh. (See 

 below.) 



Generic characters. — Marsh writes: 



The present genus is quite distinct from any of the forms 

 previously described. * * * xhe skull is large and massive, 

 with widely expanded zygomatic arches, and short and robust 

 horn cores, projecting well forward. In general form it re- 

 sembles the skull of Brontotherium but may be readily dis- 

 tinguished from it by the dental formula, which is as follows: 

 Incisors xi canines-}-; premolars |; molars |. 



The presence of four premolars in each ramus of the lower 

 jaw is a distinctive feature in this genus. This character, with 

 the single, well-developed incisor, marks both the known species 

 [B. robusius, B. dispar]. 



FitiUHE 179. — Tj'pe (holotype) skeleton of Brontops, robusius 

 Yale Mus. 12048. After Marsh, 1889. One twenty-fourth natural size. 



to tip. In side view the horns completely overhang the nasals 

 and are slightly recurved. The long axis of the horn section is 

 [almost or quite] directly transverse. 



Measure7nents 



Millimeter.'! 



Outside length of horns 315 



Transverse diameter of horns 125 



Anteroposterior diameter of horns . 67 



The type probably belongs to a young male in which the 

 horns are not fully developed, because the horns increase in 

 width and flatness and the basal section becomes more truly 

 transverse, with age. 



Etymology. — irXarvs, flat; /cepas, horn. 

 Present determination. — This valid species, described 

 on page 578, belongs in the genus Brontotherium. 



Etymology. — Brontotherium; &^, face, "having the 

 face or appearance of"; resembling Brontotherium. 



Present determination.— In 1902 Osborn (1902.208) 

 treated Brontops as a synonym of Megacerops Leidy, 

 but renewed examination of Leidy's figure of M. 

 coloradensis indicates that it is not congeneric with 

 Brontops, which is here regarded as a valid genus. 



Brontops robustus Marsh, 1887 

 Cf. Brontops robustus, this monograph, page 492 

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

 p. 326, October, 1887 (Marsh, 1887.1). 



Subsequent references. — Restoration of Brontops ro- 

 iustus: Am. Jour. Sci., 3d ser., vol. 37, pp. 163-165, pi. 



