522 GEOLOGICAL SURVEY OF THE TERRITORIES. 



exactly a space equal to that supporting the last four of A. megalodus. 

 The last molar is larger than the penultimate in A. crassum, (larger in 

 A. megalodus,) and encroaches on the base of the coronoid process ; in 

 all the jaws of A. megalodus, this tooth is considerably in advance of this 

 process, which rises more abruptly than in it. This tooth is shown to 

 be the last molar by the absence of any trace of alveolus or crown of a 

 successioual tooth behind it in the various jaws in question. In A. eras- 

 sum, the coronoid process rises grad^ially from the front of the last molar. 



Measurements. 



A . msgalodu. A . erassits. 



Length of last four molars 0.160 0.215 



Length of last molar 044 .062 



Length of first true molar 036 .055 



Width of first true molar , 028 .033 



Depth of ramus at M. 2 087 .078 



Width of ramu8atM.2 047 .055 



The last molar is not quite protruded in the type specimen of A. eras- 

 sum. 



ISfear to the specimen just described, I found the left maxillary bone, 

 ■with nasal, frontal, and other elements, of a rhinoceros, which differ in 

 some respects from corresponding parts of A. megalodus. The rather 

 larger teeth would coincide with the type of A. erassum; but that the 

 specimens belong to the same individual is not certain. It is charac- 

 terized by the same increase in size posteriori}^ of the molars ; the M. 2 

 exceeding that of the A. megalodus, while the P. m. 2 (the first) is consid- 

 erably smaller. The latter measures less than half M. 2, while it is 0.8 

 the diameter of the same in the A. megalodus. There is no rudiment of 

 P. m. 1. Hence, this specimen displays fully the characters of the 

 genus Aphelops. The nasal bones are long, acuminate, straight, and not 

 co-ossified. They are tectiform, and distally compressed, instead of 

 flattened, as in two specimens of the A. megalodus ; they are also quite 

 rugose at the extremity. These characters may be only sexual. 



HIPPOTHERIUM, Kaup. 



HiPPOTHEEiUM SPECiosuM, Leidy, Anc. Fauna Dak. and Neb., 282. 



HiPPOTHERIUM PANIBNSE, sp. UOV. 



Indicated by molar teeth in the collection. Two of these have elongate- 

 curved crowns ; the longer is a left posterior, the more abraded a right 

 median. The latter is characterized by the generally greater simplicity 

 of the enamel-boundaries of the lakes, as compared with the same por- 

 tions of S. speciosum, with which it agrees in size. The only plications 

 to be observed are the usual opposite ones entering the lakes from the 

 middle of their adjacent boundaries, and a slight one at the inner angle 

 of the same border of the anterior lake. The inner crescents are united, 

 the posterior retaining its width posteriorly, and giving off the posterior 

 inner column from its anterior half. Both the internal columns are lon- 

 gitudinally oval and rather small, the anterior well separated. The ad- 

 jacent en am el -border gives off the usual projecting fold. Outline of crown 

 nearly quadrate. 



A second molar, less worn, presents therefore a little greater com- 

 plexity of enamel-folds. Thus the anterior inner part of each lake is 

 folded into a loop, and there is a second pair of opposite folds outside 

 of the usual pair on the adjacent borders of the lakes. 



A third molar is much more worn than either of the preceding, so as 



