16 Annals of the Carnegie Museum. 



face of the trigonid is nearly perpendicular. The anterior cusp is 

 antero-posteriorly compressed and is oblique. It is somewhat cingu- 

 lum-like in form. The heel is short antero-posteriorly and is com- 

 posed of three distinct cusps. 



mm. 



Length of molar .-. 2.4 



Height of trigonid of molar 3.4 



A lower molar (No. 1691, Plate I, Figs. 1-2) probably belongs to 

 the Cimolestidse. The trigonid was composed of two prominent cusps 

 and an anterior conule. One of the cusps is broken off at the base. 

 The remaining cusp is high and curves backward toward the apex. 

 The anterior conule is well defined. The heel is separated by a trans- 

 verse valley from the trigonid and it has three small, low, blunt, nearly 

 equal-sized tubercles. 



mm. 

 Length of molar 3.25 



Cimolestes? Marsh, 



(Plate I, figure 16.) 



(Am. Jour. Sc. (3), XXXVIII, 1S89, p. 89.) 



The left ramus of a mandible (No. 10 13), is referred provisionally 



to this genus. It has the alveoli of the molars and premolars, but no 



tooth, except a somewhat injured last molar. Ten comparatively large, 



transversely oval alveoli are shown anterior to M3-. The alveolar 



border of the mandible is nearly straight and the anterior portion of 



the coronoid process ascends abruptly. The lower border of the jaw 



is somewhat convex. The heel of the last molar is low and has three 



low, blunt tubercles. Associated with Ptilodtis, Chirox, crocodile 



teeth, etc. From Silberling quarry east of Bear Butte, Montana. 



mm. 



Length of M.^ 2.9 



Length of portion of mandible preserved 22.0 



Depth of mandible under M^ 5.4 



Family DIDELPHYID^ Gray. 

 Peratherium ? Aymard. 



(Ann. Soc. Agr., Sci., Arts et Comm. du Puy, XIV, 1850, pp. Si, 83-84.) 

 Number looi, Carnegie Museum Catalogue of Vertebrate Fossils, 

 is a fragment of a mandible with one nearly perfect molar tooth, which 

 considerably resembles the second lower molar oi Peratherhivi alternans 



