228 ON THE EXTINCT MAMMALIA OF 



at condyles, five inches ; breadth of articular surface of condyles, four inches ; breadth 

 of trochlea for the patella, two inches. 



The head of a tibia, from the collection of Dr. Evans, has the following measure- 

 ments : breadth of head of tibia, four inches ; width fore and aft and internally, three 

 and a half inches. 



Rhinoceros crassus. 



Some fossil remains, consisting of small fragments of jaws with portions of teeth 

 and several isolated teeth, discovered by Dr. Hayden in the sands of the L'eau-qui- 

 court, or Niobrara River, have been referred to a species of Rhinoceros with the above 

 name, though it is uncertain whether all the specimens belong to the same species. 



The more characteristic specimens consist of a fragment of the upper jaw containing 

 the greater portion of a last molar tooth, and an isolated upper lateral incisor. These 

 appear to indicate a species of about the same size, and having the same formula of 

 dentition as the existing Indian Rhinoceros. 



The portion of the upper molar tooth, represented in figure 8, plate XXIII, is of 

 the right side, and exhibits the modification of form from the other true molars which 

 is usual in living species of the genus. The specimen nearly agrees in size and con- 

 struction with the corresponding portion of the same tooth in the Indian Rhinoceros. 

 The crown is about a third worn away, and when perfect has measured fore and aft 

 internally about two inches, and its oblique diameter postero-externally has been 

 about half an inch more. From the corresponding tooth of R. occidentalis it not only 

 differs greatly in size, but the posterior lobe of the crown presents an offset projecting 

 into the transverse valley, opposite the similar but lesser offset or bulge of the anterior 

 lobe. A prominence occupies the bottom of the inner half of the transverse 

 valley. 



The isolated upper lateral incisor, represented in figures 6, 7, is of the left side, and 

 nearly agrees in its proportions and size with the corresponding tooth of the Indian 

 Rhinoceros. The crown is much worn away, the abrasion having extended nearly to 

 the base externally, and beyond or above it internally. The worn surface, figure 7, is 

 a long ellipse, measuring two and a third inches fore and aft, and three-fourths of an 

 inch transversely. 



The remaining specimens attributed, with less certainty, to R. crassus, consist of a 

 fragment of a lower jaw with the first large temporary molar, and the isolated crown 

 of an upper temporary premolar. 



The first mentioned specimen is represented in figure 9, and nearly agrees in its 

 form with the corresponding portion of the lower jaw of a young Indian Rhinoceros, 

 though the contained tooth is relatively larger. The anterior end retains the bottom 

 of a lateral incisive alveolus, and leaves sufficient space to have been occupied by a 



