316 
PERISSODACTYLA. 
ductus very closely, and may belong to it; the figure is that of a cast sup¬ 
posed to be derived from a North American specimen. A fragm’ent of 
another tooth from Tarborough, N. C., believed to be, like the Maryland speci¬ 
men, fi’om the Miocene marl, may belong to the M. obscurus or similar species. 
The formation alluded to has been usually correlated with the White Eiver 
Miocene of the West, Avhich preceded by a long period of time the Loup 
Fork epoch, from which the M. 'productus was derived. I must also add 
that there do not appear to be any striking characters by which the pos¬ 
terior molar teeth of the Mastodon cmdium can be distinguished from those 
of the M. productus. 
The first notice which is unquestionably of this species is that pub¬ 
lished by Dr. Leidyin the Proceedings of the Philadelphia Academy, 1872, 
p. 142. Dr. Leidy there mentioned the characters of the lower jaw, as 
seen in a specimen obtained by the Hon. W. F. Arny, governor of New 
Mexico, and sent by him to the Smithsonian Institution, Washington. The 
same specimen is fully described and figured in volume I of the quarto 
Peport of the United States Geological Survey of the Territories, by Dr. 
Leidy. 
PElilSSODACTYLA. 
APHELOPS, Cope. 
Paleontological Bulletin, No. 14, p. 1, July, 1873; Ann. Bept. Chief of Engiueers, 
1875, ii, p. 991. 
Remains of Rhinoceros are not rare in the deposits of the ancient lake 
of the Rio Grande Valley, and among the most complete fossils obtained 
is the greater part of the cranium of a species allied to the Aplielops mega- 
lodus of the corresponding beds of Colorado. The specimen includes the 
dentition of both jaAvs, Avhich exhibits the following formula: I. 1; C. 0; 
Pm. 1; M. r- The absence of the first premolar distinguishes the form from 
the Miocene Aceratherium as Avell as from the existing genus Jxhinocerus; 
Avhile the presence of inferior incisors separates it at once from the living 
Atelodus. I have named this genus Aplielops; like Aceratherium, it is horn¬ 
less. To it are referred, besides the species mentioned, the lihinocerus crassus, 
Leidy, and the A. jemezanus, first described beloAv. These are, however, 
