182 



TITANOTHERES OF ANCIENT WYOMING, DAKOTA, AND NEBRASKA 



Specific characters. — Osborn writes: 



Of more diminutive size (p'-m', 153 mm.), but the miost 

 progressive species of Palaeosyops known in the evolution of its 

 superior premolars and molars. Heavy oingula embracing the 

 inner sides of the crowns. A rudimentary tetartooone on p^. 



Etymology. — Named "in honor of the late Prof. 

 E. D. Cope, the describer of Lambdotherium, 'Palaeo- 



FiGTjRE 120. — Type (holotype) of Palaeosyops copei 

 P'-ms, right. Am. Mus. 11708. After Osborn, 1908. One-half natural size. 



syops' horealis, and other species of Eocene titano- 



theres." (Osborn.) 



Present determination. — The species is probably 



valid. 



Manteoceras washakiensis Osborn, 1908 



Cf . Manteoceras washakiensis Osborn, this monograph, page 371 



Original reference. — Am. Mus. Nat. Hist. Bull., vol. 

 24, p. 607, fig. 11, 1908 (Osborn, 1908.318). 



Type locality and geologic Tiorizon. — Base of Hay- 

 stack Mountain, Washakie Basin, Wyo.; summit of 

 UintatJierium- Manteoceras- Mesatirliinus zone (Washa- 

 kie A). 



Holotype. — A well-preserved skull with dentition 

 (Am. Mus. 13165). Discovered by Mr. Paul Miller, 

 of the American Museum expedition of 1906. (See 

 fig- 121.) 



Specific characters. — Osborn writes: 



Distinguished from M. manteoceras of a somewhat lower 

 geological level by its more progressive characters, as follows: 

 Canines short, obtuse, recurved; internal lobes of pm^, pm^ 

 broadening, with shelf for development of deuterocone; p^ (ap. 

 19 mm., tr. 17) with marked external convexities and a re- 

 duced external cingulum; p^ (ap. 19, tr. 25) exhibits 

 the tetartocone fold somewhat more conspicuously 

 than in the most progressive Bridger level D speci- 

 mens. ?■* (ap. 24, tr. 30) is progressive in transverse 

 measurement and in the development of the tetar- 

 tocone shelf. The molars are progressive in their 

 large size (m^ ap. 42, tr. 48), in the strong develop- 

 ment of the internal cingulum, and in the elongate 

 ectolophs. 



Etymology. — washaJciensis; "so named be- 

 cause it is a more recent phase, probably 

 characteristic of the Washakie rather than of 

 the Bridger." (Osborn.) 



Present determination. — The species and the generic 

 reference are valid. (See p. 371.) 



Mesatirhinus Osborn, 1908 



Cf. Mesatirhinus Osborn, this monograph, page 387 



Original reference. — Am. Mus. Nat. Hist. Bull., vol. 

 24, p. 608, 1908 (Osborn, 1908.318). 



Type species and geologic horizon. — Palaeosyops 

 megarhinus Earle. Bridger Basin, Wyo., levels Bridger 

 C and D; Washalcie Basin, Wyo., levels Washakie A 

 and base of Washakie B. 



Specific characters. — Osborn writes: 



Titanotheres of small size (skull length 354^425 mm.) 

 typically mesaticephalic, persistent or progressing to dolicho- 

 cephalic. The horns when present incipient or rudimentary, 

 chiefly borne on the nasals. An infraorbital shelf. Cranium 

 with a sagittal crest. Humerus relatively abbreviated — that 

 is, with refeYence to Palaeosyops — carpus and tarsus narrow, 

 astragalus with elongate neck, the sustentacular distal and 

 ouboidal facets continuous and forming a reversed L (j) ; meta- 

 podials slender. 



Etymology. — fiiaaros, middle; pis, nose; because the 

 length of the snout is moderate compared with that 

 in the allied genus Dolichorhinus. 



Present determination. — The genus is valid. (See 

 p. 387.) 



Mesatirhinus petersoni Osborn, 1908 



Cf. Mesatirhinus petersoni Osborn, this monograph, page 389 



Original reference. — Am. Mus. Nat. Hist. Bull., vol. 

 24, p. 608, fig. 12, 1908 (Osborn, 1908.318). 



Holotype. — A skull with dentition (Am. Mus. 12184) 

 from Cattail Spring, Bridger Basin, Wyo., levels 

 Bridger D 3 and C 3. (See fig. 122.) The species is 

 also recorded from Washalde Basin, Wyo., level 

 Washakie A. 



Specific characters. — Osborn writes: 



Pm'-m^, 156 millimeters; m'-m', 90. Skull length, pre- 

 maxillaries to condyles 412 (estimated) ; preorbital facial region 

 more elongate (217). Other characters as in Mesatirhinus 

 megarhinus — that is, broad occipital condyles, broad infra- 

 orbital shelf on malar, etc. 



Comparison of this animal with the type of M. megarhinus 

 can leave no doubt that we have to do here with a much more 

 advanced stage of evolution. The skull is longer, the pre- 

 orbital region especially. The grinding teeth occupy more 

 space, and there is an average advance in all the rectigradations 

 which proves that these differences in form and size are not 

 merely due to fluctuations of size or differences of sex. 



ffK?- 



Figure 121. — Type (holotype) skull of Manteoceras washakiensis 

 Left side. Am. Mus. 13165. After Osborn, 1908. One-flfth natural size. 



Etymology. — "The species is named in honor of Mr. 

 O. A. Peterson, now of the Carnegie Museum, whose 

 titanothere collections in the Uinta formation greatly 

 extended our knowledge." (Osborn.) 



Present determination. — The species and generic ref- 

 erence are valid. (See p. 389.) 



