262 0. C. Marsh — Description of Tertiary Artiodactyles. 



Ilomacodon vagans, 1872. 



In the Dinoceras beds of the Bridger basin, in Wyoming, 

 which may be regarded as middle Eocene, various remains of 

 Artiodactyles have been found, but none with the selenodont 

 dentition. All yet discovered still belong to the bunodont 

 division of Artiodactyla, and most of these are small in size. 

 The first genus discovered and described was Homacodon, and 

 the type specimen is the most perfect of the group yet found.* 

 In figures 5 and 6 below, the upper and lower molar teeth of 

 this specimen are represented, and in figures 7 and 8, the dis- 

 tal end of the tibia and the astragalus of the same individual 

 are also shown, all twice natural size. 



Figure 5. — Upper molar series of Homacodon vagans, Marsh ; (type) seen from 

 below. 



Figure 6. — Lower series of same individual; seen from above. 

 Both figures are twice natural size. 



The present genus has apparently the complete dentition, 

 forty-four teeth, although the type specimen does not reveal 

 the exact number of incisors. The canines are large. The 

 anterior premolars, above and below, are secant. The last 

 upper premolar has a single outer cusp and one inner cone. 

 The upper molars have each two conical external cusps. 

 There is a small median anterior cusp, also, on each. The 

 first molar has three posterior cusps, all well developed. The 

 second molar has the inner posterior cusp small, and in the 

 third molar, this is wanting, or only represented by the basal 

 ridge from which the others were derived. 



The skull of the type specimen of the present species has a 

 brain case of fair size, and a sharp sagittal crest. The orbits 

 are not closed behind. The cervical vertebrae are short, and 

 have their ends oblique, indicating a curved neck. The dorsals 

 are of moderate length, with the centra broad, and their ends 

 flat. The posterior trunk vertebrae are all keeled below. 



* This Journal, vol. iv, p. 126, August, 1872. 



