12 



cross-crests iu the last aud peuultimate molars of A. megalodiis is want- 

 ing^ in the A. crassus ; partly on this account I refer my second large 

 Pliocene rhinoceros to the latter. 



Aphelops crassus Leidy, Anc. Fauna, ISTebr., &c., p. 228. 



Leidy states that the formula of dentition of this species is identical 

 with that of the Indian rhinoceros, and elsewhere that it is probably a 

 true rhinoceros as distinguished from Aceratherium. He does not ap- 

 l)ear to have possessed material to verify these statements. 



An imperfect mandibular ramus containing the last molar and alve- 

 oli of the four teeth which precede it, differs from the corresponding 

 one of A. megalodiis iu the greater thickness in proportion to the depth. 

 It is absolutely both shallower and thicker than a corresponding ramus 

 of the allied species, w'hile the teeth are larger, the last three occupy- 

 ing exactly a space equal to that supporting the last four of A. megalo- 

 dus. The last molar s larger than the penultimate in A. crassus (larger 

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

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

 this ])rocess, 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. crassus the coronoid process rises gradually from the front of the last 

 molar. 



A. megalodiis. A. crassus. 



Length last four molars IGO .215 



Length last molar .044 .002 



Length tirst true molar 030 .055 • 



Width first true molar .... .028 .033 



Depth ramus at m. 2 087 .078 



Width ramus at m. 2 1047 .055 



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

 crassus. 



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

 with nasal, frontal, and other elements of a rhinoceros w-hich differ in 

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

 larger teeth would coincide with the type of A. crassus, but that the 

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

 ized by the same increase in size posteriously of the molars, the M. 2 

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

 ably smaller. The latter measures less than half M. 2, while it is .8 the 

 diameter of the same iu 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 coos- 

 sified. They are tectiform, aud distally compressed, instead of flattened, 

 as in two specimens of A. megalodus ; they are also quite rngose at the 

 extremity. These characters may be only sexual. As in A. megalodus, 

 they did not support a horn. 



HiPPOTHEEiUM SPECiosuM Liedv, Anc. Fauna, Dakota, Nebraska, 

 p. 282. 



HiPPOTHEElUM PANIENSE, Sp. UOV. 



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

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

 a right median. The latter is characterized by the generally greater 



