198 BULLETIN UNITED STATES GEOLOGICAL SURVEY. [Tol.Yl. 



elude four premolars (the first one-rooted), so that the formula M. | f is 

 that of Facliynolophus Pom. rather than of LopModon. I refer another 

 species to the same genus, by analogy, as it agrees in the dentition of 

 the inferior jaw. 



39. Hyracotheeium angxjstidens Cope. 



Apparently an abundant species. There are three sizes which I refer 

 here, which may represent difierent species, but this cannot be deter- 

 mined without better material : 



A. Depth of ramus at last premolar or first true molar, .0120 ; length 

 of crown of first true molar, .0070 ; length of last true molar, .0100. 

 Lower jaw of one specimen. 



B. Depth of ramus, .0140 ; length of first true molar, .0065 ; of last 

 molar, .0100. One lower jaw. 



C. Depth of ramus, .0155 ; length of first true molar, .0075 ; of last 

 true molar, .0100. Two individuals. 



Portions of lower jaws of three other individuals in the collection are 

 apparently referable to the H. angustidens. 



40. Hyracotherium venticoluh sp. nov. 



Hyracother'mm vasacciense Cope, American Naturalist, 1880, p. 747 ; not Report 

 Expl. Surv. W. of lOOth Mer, iv, p. 264. 



Eepresented by an entire skull, with some bones of the skeleton, of 

 one individual. 



In general, this species is to be distinguished from its near ally, the 

 S. vasacciense, by the slender mandibular ramus. The depth of this 

 bone is about equal to that found in the larger varieties of the R. angus- 

 tidens, but the teeth are much larger, having the proportions of those of 

 the H. vasacciense. This remark applies especially to the last inferior 

 molar. 



The inferior canines form part of an uninterrupted series with the 

 incisors. The superior canine is separated from the superior incisors 

 by a diastema. The first premolar in both jaws is isolated. The second 

 superior premolars have two cusps, and an internal ledge posteriorly. 

 The third and fourth superior premolars are similar, the fourth display- 

 ing a little larger transverse diameter. The true molars are of subequal 

 dimensions. Their external cusps are subconic. All the molars except 

 the first and second premolars are entirely surrounded by a basal cin- 

 gulum, which rises into a low cusp at the anterior external angle of the 

 crown. The third inferior premolar has its two median cusps well 

 separated and a wide posterior heel. The heel of the last premolar is 

 wider, but carries no internal cusp. The external cusps on all the teeth 

 wear into well-defined Ys. The posterior five molars have an external 

 basal cingulum, but no other. 



The mandibular ramus is compressed. The ascending ramus rises 

 almost vertically a short distance posterior to the last molar. The sym- 

 physis is narrow, and extends to below the middle of the first premolar. 

 The infraorbital foramen opens above. 



