RHINOCEROS. ' 81 



Rhinoceros Occidentalis, Leidy. 



(Plates XIL, XIII.) 



Rhinoceros occidentalis, Leidy: Proo. Acad. Nat. Soi., 1850, v., 119; lb. 1851, 276; Owen's Rep. of a Geol. 



Surv. of Wise, etc., 552. 

 Aceratherium, Leidy: Proc. Acad. Nat. Sci., 1851, v., 331. 



The materials which we have in possession to describe the larger species of Rhi- 

 noceros from Nebraska, are as follows : — 



1. A skull, with the right superficial portion and end of the nose broken away, 

 and otherwise much fractured and mutilated. It contains upon the left side all 

 the molar teeth except the tirst, which fortunately exists upon the other side ; but 

 all the remainder are broken. From the collection of Dr. D. D. Owen. 



2. Two fragments of lower jaws, from two other individuals; one containing the 

 last two molars, the other the posterior three molars, except the last. From Dr. 

 Owen's collection. 



3. Nine fragments of as many upper molars, and eight small fragments of lower 

 jaws, only two of which contain perfect teeth; apparently from three or four dif- 

 ferent individuals. From the collections of Messrs. Culbertson and Capt. Van Vliet. 



The species was originally established upon several small fragments of molar 

 teeth, procured by Mr. A. Culbertson, and its existence was afterwards confirmed 

 by several entire molars brought home by Mr. T. A. Culbertson. 



Description of the Skull. — The skull in the collection of Dr. Owen, is about three- 

 fourths the size of that of the Rhinoceros indicus. Its upper part and left side, with 

 the corresponding molar teeth, are comparatively well preserved. The specimen is 

 an adult one, though it did not belong to an old individual, for all the molars are 

 protruded, but in none is the enamelled triturating surface obliterated. 



Lateral View. — (PI. XII. Fig. 2.) One of the most remarkable features of the 

 species is presented in the side view of the skull, viz. : the verticality of the inion, 

 with the slight degree of inclination forward of the upper part of the head. In- 

 deed, the latter is so nearly horizontal, that, in comparison with the skull of Rhino- 

 ceros indicus, it appears as if the two extremities of the head had been depressed, or, 

 in other words, as if the head had been forcibly made straight. In connection with 

 the peculiarity just described, a relatively large proportion of the temporal fossa is 

 situated posteriorly to the root of the zygomatic process, which holds a position 

 about the middle of the fossa, whereas in Rhinoceros indicus it is placed at the pos- 

 terior third of the latter. 



The zygomatic process extends from its root less outwardly, but rises more than 

 in Rhinoceros indicus. Its upper margin slopes forward more than in the latter, 

 and the upper surface of its root is nearly horizontal. The outer surface is vertical 

 and convex; but anteriorly, or where the malar bone contributes to the formation 

 of the zygoma, it is flat. The deepest part of the zygoma is just in advance of the 

 glenoid articulation, and measures about two inches. 



The meatus auditorius is vertically ovate, with the narrow part downward. 



The temporal fossa has almost the same relative extent as in Rhinoceros indicus, 



