384 E. L. Troxell — American Bothriodonts. 



by enamel that, once the wearing- starts, the tooth goes 

 rapidly, allowing the one opposing to remain practically 

 nneroded. 



Elomeryx armatus angustus, subsp. nov. 



(Fig. 5.) 



Holotype, Cat. No. 10393, Y. P. M. Upper Oligocene (Protoceras beds), 

 Hermosa, South Dakota. 



This new subspecies may be distinguished by the moder- 

 ately long postcanine diastema, 25 mm. ; the very narrow 

 P2, 9.5 X 16 mm., and P^ 14.5 X 20.5 mm. P^ is of 

 moderate proportions, concave anteriorly, and has a 

 shallow, narrow longitudinal groove. On the molars the 

 cingula surround the hypocones and, except for slight 

 breaks, the protocones. The styles on the outer sides of 

 the molars are well marked by deep indentations and on 

 M^ all are prominent. The transverse valley curves 

 backward strongly and ends in a narrow angle on the 

 mesostyle. 



The postglenoid process is rather narrow, pointed, and 

 does not curve strongly forward. The occipital condyles 

 are not wide nor thick, but the median ventral groove is 

 broad. The moderate otic bullae and the little worn teeth 

 show an animal just reaching maturity. 



This specimen differs from the type of E. mitis^^ in 

 that the latter has no cingula on the internal slopes of 

 the hypocone and protocone and also has a weaker, more 

 pointed parastyle with a single groove and no secondary 

 cusp on its posterior side. 



^pinacodon,'^^ gen. nov. 



A name is proposed at this time for a genus to include 

 those American forms widely separated from Elomeryx, 

 Octacodon, and Heptacodon Marsh, and may include 

 Eyopotamus americmius Leidy 1856, H. deflectus Marsh 

 1890 (the genoholotype), and Ancodon rostratus Scott 

 1895." 



These constitute a group of bothriodonts of a much 



^^ The main feature on which this species was made — its smaller size — was 

 chosen as a result of a misinterpretation on the part of Professor Marsh. 

 His so-called first molar is the last deciduous tooth, as proved by the pres- 

 ence of P* underneath it. Therefore the last tooth present is M^* and is 

 found to be as large as that of the genoholotype. It is worth noting that 

 the last milk tooth is molariform in every respect. 



"AtTretj/os, high; dKri, point; odovs, tooth. 



