Cope.] 160 fDec. 16, 



shorter than the external. The fourth premolar is relatively shorter than 

 in any other species of the genus, and the posterior marginal lobe is a mere 

 thickening of the edge of the heel. There is a low anterior basal tubercle. 

 The enamel is smooth. 



The ramus is compressed and not deep. The angle is prominent, and is 

 not inflected ; it does not extend so far posteriorly as the posterior border 

 of the condyle. The inferior border of the masseteric fossa is an angular 

 line, without abrupt excavation, but the face of the fossa descends rapidly. 

 The anterior border of the fossa is abrupt and is formed by the usual sub- 

 vertical ridge. 



Measurements. M. 



Length between P-m. IV, and condyle inclusive 0520 



" of posterior three molars 0170 



" of tubercular-sectorial 0070 



Elevation of " " 0070 



Depth of ramus at sectorial . 0100 



DlDYMICTTS CURTIDENS, Sp. UOV, 



As in the case of the D. massetericus the present species is represented 

 by a single fragmentary mandibular ramus. This supports a sectorial tooth 

 of the size and form of that of the D. protenus, and is thus much larger 

 than that of the species just named. This tooth is placed nearer to the 

 base of the coronoid process than is seen in any other species, and only 

 leaves space for a short tubercular tooth. This is lost from the specimen, 

 but the alveolus shows pretty clearly its dimensions. The base of the 

 fourth premolar remains, and it is evident that this tooth was like that 

 of D. protenus in form and proportions. The base of the posterior marginal 

 lobe is present. The ramus is deeper and larger than in the D. massetericus. 



Measurements. M. 



Length of bases of last three molars ■ ( . . .0285 



". fourth premolar 0120 



" of sectorial on base 012 



Width " in front .008 



Depth of ramus at sectorial 017 



Ictofs bicuspis Cope. Bull. U. S. Geolog. Surv., Terrs. 1881, p. 192. 



This mammal was founded on a skull from the Wind River region. 

 It is now represented by a mandibular ramus. The form of the fourth 

 premolar being unknown, its reference to this species is provisional only. 

 It may be remotely allied to Stypolophus, but the anterior inner cusp of the 

 molars is small and does not reach the inner side of the crown, and the an- 

 terior external cusp is but little larger than the second anterior inner. The 

 two cusps last named stand opposite to each other, and their apices are only 

 separated from each other by an open notch. They, with the first anterior 

 inner (here median), form a transverse narrow triangle. The posterior 

 part of the crown is rather large and, though lower than the anterior part, 



