1881.) 397 [Cope. 
Fic. 2. Part of right maxillary bone of Meniscotherium chamense Cope, from 
the Wasatch bed of New Mexico. From Report Capt. G. M. Wheeler, IV, ii, 
Pl. LXVI. 
MENODONTID 2. 
The known genera of this family are not numerous. They are defined 
as follows: 
I. Vs of inferior molars probably incomplete ; superior molars with in- 
termediate tubercles. 
Internal cusps of superior molars well separated..............05 Acoéssus. 
II. Inferior molars with the crowns thrown into two Vs; superior 
molars without intermediate tubercles. 
a, Last superior premolar only with two inner tubercles. 
Incisors present..... sare eal aemarameateca alta Nese ava le eda ach cectase eta Diplacodon. 
aa, All the superior premolars with two interior cusps. 
Six inferior incisors, canines very large........ Jon Seats Sew ees Deodon. 
Six inferior incisors ; canines very small........ ......-.2-.0.. Menodus. 
No inferior, and four small superior incisors ; canine very small.......... 
Symborodon. 
The first appearance of this family was in the Early Eocene in the genus 
Acoéssus Cope, which was a cotemporary of Hyracother’um, and which it 
resembles in some respects. Its typical species was called Hyracotherium 
siderolithicum by Pictet, its describer, but Kowalewsky has already ex- 
pressed the opinion that the species does not belong to that genus. It is 
from the Lower Eocene of Mauremont, Switzerland. The remaining 
genera are, as yet, American, excepting one, which is represented by an 
Austrian species, not yet well known. Diplacodon, in its simpler pre- 
molars, approaches the Chalicotheriide, and is the oldest of the American 
genera. Itis fromthe Uinta or Upper Eocene. Menodus and Symborodon, - 
which include some species of gigantic size, belong in the White river or 
Oligocene, while Deodon has so far only been obtained from the Truckee 
or Upper Oligocene. 
