Douglass : Vertebrate Fossils from Fort Union Beds. 19 



The molar is quite peculiar. The anterior trigon is composed of 

 three distinct cusps, of which the postero-external one is the larger and 

 the anterior one the smaller. The heel of the tooth is much larger 

 than the anterior portion. It is bounded externally by two tubercular 

 cusps, while the posterior and internal borders form sharp ridges which 

 meet at the postero-internal angle of the tooth forming a right angle. 

 At this angle is a little thickening suggesting a rudimentary cusp. 

 From Silberling quarry east of Bear Butte, Montana. 



mm. 



Length of the two teeth preserved 2.7 



Depth of mandible 2.7 



Order GLIRES? {RODENTIA) Linnaeus. 



Family MIXODECTID^? Cope. 



Mixodectes? Cope. 



(Am. Nat., XVII, 1883, p. 191.) 

 (Plate II, figures 9-10.) 



One specimen (Carn. Mus. Cat. Vert. Fos. , No. 1672) I am unable 

 to assign with certainty to any genus that has been described, so I 

 place it with much doubt in the genus Mixodectes. The specimen 

 consists of two teeth in a portion of a mandible. They are so much 

 worn that the exact original pattern of their crowns cannot be made 

 out, but each had three cross-crests which were united on the outer 

 portion of the tooth thus forming a figure something like a W, or an 

 M. The large amount of wear indicates that the animal subsisted on 

 hard substances, undoubtedly of a vegetable nature. From Silberling 

 quarry east of Bear Butte, Montana. 



Another lower molar (No. 1936) apparently belongs to the same 

 genus. It is less worn and the anterior portion is higher than the 

 posterior portion. 



A portion of an incisor tooth (Plate I, Figs. 18 and 20) in the col- 

 lection loaned by Mr. Silberling very strongly suggests that of a rodent. 

 The tooth is broad antero-posteriorly and compressed laterally. The 

 point is broken off. The tooth curves in the same manner as those of 

 rodents. The anterior and posterior edges are rounded, making a 

 cro^s-section of the tooth an oblong ellipse. The anterior face of the 

 tooth is covered with enamel which overlaps one of the lateral surfaces 

 more than the other. 



