36 GEOLOGICAL SURVEY OF TEXAS. 



Measurements of Mandible. 



Mm. 



Length from heel of last molar to iucisive alveolus 143 



Length from heel of last molar to symphysis Ill 



Length from heel of last molar to canine 123 



Length of molar series 84 



Length of true molars 43 



Length of third premolar 14 



Wiflth of third premolar 9 



Length of first true molar 13 



Width of first true molar 10 



Length of last true molar 19 



Width of last true molar 8 



HIPPOTHERIUM, Kaup. 



Cope, Proceeds. Amer. Philosop. Society, 1889, p. 429. 



Hipparion^ Christol. ? Merychippus and Anchippus, Leidy. 



Species of this genus are much less abundant in the Loup Fork beds of 

 Donley county than those of Protohlppus, and these belong to the larger 

 forms. 



HIPPOTHERIUM AFFINE, Lcldy. 



Extinct Mamm. Dakota-Nebraska, 1869, p. 286, pi. XVIII, figs. 20-24. 

 Hippotherium occidentale, Cope, Proceeds. Amer. Philos. Society, 1889, 

 pi. I, fig. 1 (not of Leidy). 



A single superior molar found. 



HIPPOTHERIUM OCCIDENTALE, Leidy. 



Proceeds. Acad. Phila., 1858, p. 27. Hipparion occidentale, Leidy, op. 

 cit., 1856, p. 59; Extinct Mamm. Dakota-Nebraska, pp. 281, 326, pi. 

 XVIII, figs. 1-5; pi. XXVI, fig. 2. 



A fragment of a maxillary bone with four molars, and some bones of 

 the skeleton of one individual; and a single superior molar of a second 

 individual. These present the superior degree of complexity at an age 

 at which the enamel plates are comparatively simple in the H. affine, as 

 pointed out by Leidy. 



PEOCAMELUS, Leidy. 



I have before me jaws of five species of this genus, and the examina- 

 tion of these, with previous examinations of other specimens, leads me to 

 define the former as follows: 



I. Mandibular ramus at M. ii, about three times as deep as the eleva- 

 tion of the crown of M. ii, above alveolar border. 



a. Premolar series short, equal two columns of last inferior molar. 



