408 Bulletin American Museum of Natural History.  [Vol. XXXIV, 
Microsyops Leidy 1872. 
Type, M. gracilis Leidy, from Lower Bridger of Wyoming. 
The Bridger species are all distinguished by equal height of the two outer 
cusps (protocone and deuterocone) of p*, and of the two trigonid cusps, 
protoconid and deuteroconid, of ps. These, with the broader and more 
distinctly bicuspid basined heel of ps, and presence of a strong curved crest 
on the same tooth in the position of the paraconid of the true molars, are 
the only generic distinctions which I can make from Cynodontomys. But 
M. scottianus of the Wind River agrees with Cynodontomys in all except the 
broader heel of ps, and even this is not so distinctly bicusped as in the 
Bridger species. It should be transferred to Cynodontomys. This leaves 
Microsyops as an exclusively Middle Eocene genus. 
2, > 
— 5 
7 L———— ASS 
aa 
a TA Z L Agi 
Wy Ag God 
Fig. 38. Microsyops elegans, upper jaw, outer and crown views. Bridger beds (Middle 
Kocene), Bridger basin, Wyoming. M1! and part of p‘ drawn from No. 12592. 
Discussion of ordinal affinities. The molar teeth of Microsyops and 
Cynodontomys are not unlike those of the Eocene Tarsiide in construction. 
The lower molars have small triangular trigonids somewhat constricted off 
from the large basined talonids. The paraconid is distinct but low; in the 
Anaptomorphide, when distinct, it is more nearly on a level with the other 
cusps. The hypoconulid is distinet on mj-2 while in Tarsiidee it is usually 
absent; on mg the entoconid is a distinct cusp, while in most Tarsiide it is a 
