228 



TITANOTHERES OF ANCIENT WYOMING, DAKOTA, AND NEBRASKA 



Eocene the present genus may be distinguished by having 

 only three lower premolars on a side instead of four. * * * 



Of the three lower incisors in place on each side, the middle 

 one is the largest. There is a short diastema behind the 

 lower canine, but no first premolar. The dental formula of 

 the lower jaws is as follows: Incisors, 3; canine, 1; premolars, 

 3; molars, 3. 



The space occupied by the lower dental series is 143^ inches, 

 and by the last three molars 8H inches. 



Etymology. — reXeos, distant; dSovs, tooth; in allusion 

 to the peculiar character of the incisors. 



Present determination. — The genus may either be 

 valid or synonymous with an early stage in the evolu- 

 tion of Brontops. 



Teleodus avus Marsh, 1890 



Cf. Teleodus avus, this monograph, page 481 



Original reference. — Am. Jour. Sci., 3d ser., vol. 39, 

 pp. 523, 524, June, 1890 (Marsh, 1890.1). 



Type locality and geologic horizon. — " BrontotJierium 

 beds of Dakota" ( = Chadron formation, or Titano- 



therium zone) ; exact 

 geologic level not re- 

 corded but probably 

 lower beds (Chad- 

 ron A). 



Type . — A lo wer j aw. 

 Yale Mus. 10321. 

 (See fig. 188.) 



Specific cliaracters. — 

 Not separated by 

 Marsh from the gen- 

 eric characters. (See 

 Type ol Teleodus avus p. 481.) 



Etymology. — avus, 

 grandfather; in allu- 

 sion to the primitive character of the animal. 



Present determination. — The species is probably 

 valid. 



Allops crassicornis Marsh, 1891 



Cf. Allops crassicornis, this monograph, page 517 



Original reference. — Am. Jour. Sci., 3d ser., vol. 42, 

 p. 268, September, 1891 (Marsh, 1891.1). 



Type locality and geologic horizon. — "BrontotJierium 

 beds of South Dakota" ( = Chadron formation, or 

 Titanotherium zone). Geologic level as recorded by 

 J. B. Hatcher, collector, is the lower portion of the 

 upper Titanotherium zone (Chadron C). 



Type. — A "nearly perfect skull of an adult but not 

 old animal." Nat. Mus. 4289. (See fig. 189.) 



Specific characters. — Marsh writes: 



The skull is of medium size, with the zygomatic arches moder- 

 ately expanded. The nasal bones do not project beyond the 

 premaxillaries. The horn cores are very short and massive, 

 with rounded summits, and thus form one of the striking fea- 

 tures of the skull. The dentition is complete and in fine pres- 

 ervation. The single incisor is quite small and situated close 



Figure 188.- 



Lower incisors and canines, 

 natural size. 



to the canine. The latter is of moderate size and projects 

 but little above the rest of the dental series. There is no 

 diastema between the canine and the first premolar, which is 

 small and has its inner face on a line between the canine and 

 the second premolar. The second, third, and fourth premolars 

 are large and have a strong inner basal ridge. The last molar 

 has its anterior margin somewhat in advance of the front 

 border of the posterior nares. 



The length of this skull on the median line is about 30 

 inches, and the width across the zygomatic arches 23 inches. 

 The width across the horn cores is 14 inches. The extent of 

 the superior dental series is 16 inches. 



Etymology. — crassus, thick; cornus, horn. 



Present determination. — The species is valid. It is 

 fully described on page 517. 



Brontops validus Marsh, 1891 



Cf. Brontops dispar, this monograph, pages 230, 488 



Original reference. — Am. Jour. Sci., 3d ser., vol. 42, 

 p. 269, September, 1891 (Marsh, 1891.1). 



Type locality and geologic horizon. — The geologic 

 level as recorded by J. B. Hatcher, collector, is the 

 "middle portion of the middle Titanotherium beds, 

 White River, S. Dak." (Chadron formation, horizon 

 Chadron B). 



Type. — A "skull in fine preservation." Nat. Mus. 

 4290 (skull K). (See fig. 190.) 



Specific characters. — Marsh writes: 



[The skull] agrees in its main characters with the other 

 species of the genus but is particularly short and robust. The 

 zygomatic arches are widely expanded, almost as much as in 

 any skull of this group. The nasal bones have only a moderate 

 extension in front and do not reach the end of the premaxil- 

 laries. The free portion is broad and massive. The horn cores 

 are of moderate size, nearly round in section, and have their 

 obtuse summits directed somewhat backward. The occipital 

 crest slopes forward and is expanded transversely. The length 

 of this skull on the median line is about 26 inches. The great- 

 est transverse diameter across the zygomatic arches is 22 inches, 

 and across the summits of the horn cores 14 inches. 



Etymology. — validus, stout, brave. 

 Present determination. — As shown on page 202, this 

 species is probably synonymous with Brontops dispar. 



Titanops medius Marsh, 1891 



Cf. Broniotherium medium, this monograph, page 573 



Original reference. — Am. Jour. Sci., 3d ser., vol. 42, 

 p. 269, September, 1891 (Marsh, 1891.1). 



Type locality and geologic horizon. — "Near the top of 

 the Brontotherium beds of South Dakota" (Chadron 

 formation, Titanotherium zone). J. B. Hatcher, col- 

 lector. 



Type. — "One skull in fair preservation with the 

 horn cores and dentition complete." Nat. Mus. 4256. 

 (See fig. 191.) 



Specific characters. — Marsh writes: 



The free portion of the nasals is very small and projects but 

 slightly beyond the anterior line of the horn cores. The latter 

 are compressed anteroposteriorly and project laterally nearly 



