146 
MESODONTA. 
Pantolestes chacensis, Cope. 
Plate xlv, fig. 17. 
System. Cat. Vert. Eocene New Mexico, U. S. Geog. Survs. W. of lOOtli M., 1875, p. 15. 
The mandibular ramus of this species is very slender in both vertical 
and transverse diameters. There is a minute tubercle on the anterior base 
of the fourth premolar. There is a very minute median tubercle on the 
posterior border of the first and second true molars, and no anterior ledge. 
The heel of the last, molar is short, and the other tubercles protuberant. 
The enamel is smooth, and there is no basal cingulum on either side of the 
teeth preserved. 
' Measurements. 
M. 
Length of the bases of seven molars... . 0. 037 
L.mgth of the bases of three true molars.. ...... 0. 018 
Length of the base of the last premolar .... 0. 005 
Width of the same. 0.0025 
Length of the penultimate molar_ .... .. 0.0055 
Widtli of the same....... 0. 0040 
Length of the last molar... 0.0070 
Width of the s i me.... 0. 0040 
Depth of the ramus at the fourth premolar. 0. 0080 
This species is considerably larger than the type of the genus, P. longi- 
caud'us, Cope. (See Ann. Eep. U. S. Geol. Surv. Terrs., 1872, p. 549.) 
APHflLISCUS, Cope. 
System. Cat. Vert. Eocene New Mexico, U. S. Geog. Survs. W. of 100th M., 1875, 
pp. 13-10. 
The present genus is nearly allied to Pantolestes, but differs in the 
absence of the heel of the last inferior molar and tlie simplicity of the 
inner anterior tubercle of all the molars. The characters of the inferior 
molars are as follows: Premolars, four; molars, three; the latter subequal 
in size. Premolars compressed, the fourth with a heel, but no internal 
tubercle. Last two molars with four subequal angular cusps, connected 
round a central concavity by their adjacent angles. Symphysis mandibuli 
persistent. 
The affinities of this genus cannot now be ascertained, but the molar 
teeth are so much like those of the Lemurine genus Anaptomorpirns, Cope, 
