304 Bulletin American Museum of Natural History. [Vol. XVI, 



posterior direction of the internal upper and external lower 

 enamel inflections, on which Professor Scott largely relies to 

 distinguish the species. Two anterior fossettes are preserved 

 on p*, while the posterior fossette has already disappeared. 



6. S. hesperus. Founded on the lower jaw of a young in- 

 dividual which is certainly close to 5. montanits if not identical ; 

 the difference in age prevents any accurate comparison. The 



size is the same at similar 

 points of wear; the upper 

 <^ yfl^ /\ f 7/^\\/f_/// A/(f\L^<^l incisors are more rounded 



externally, but the value of 

 this character is doubtful. 



Fig. 9. Steneofiber hesperus. Lower molars x ?. The depth and Complexity 

 Type. White River, Montana. r , 1 i r 1 i 



01 the enamel folds, as 

 nearly as I can judge on the specimens, correspond fairly well. 



7. S. complexus. Founded on the anterior half of the skull 



and jaws of an animal 

 younger than any of the 

 preceding types, still re- 

 taining the milk premolars. 

 The skull has the long, 

 slender muzzle of S. ne- 

 brascensis; the postorbital 

 constriction is moderate, 

 and the temporal crests do 

 not unite into a sagittal 

 crest, but are separate, as 

 in 5. gradatus. The differ- 

 ence in wear precludes comparison of the teeth with those 

 of the remaining species; the dimensions of the masseteric 

 scar and coronoid process given by Mr. Douglas as distinguish- 

 ing characters likewise change with age so much as to be un- 

 safe specific distinctions. The separate temporal crests may 

 constitute a valid specific distinction. 



Eucastor (Leidy) Allen. 



This genus is represented by a single species found as yet 

 only in the Nebraska Loup Fork. The teeth are considerably 



Fig. 10. Steneofiber cotnplexus. Upper and 

 lower molars, x \. Type. White River (?), 

 Montana. 



