56 The American Naturalist. (January, 
GEN. LAMBDOTHERIUM Cope. Incisors chisel-shaped. Premolars 
relatively reduced, a wide diastema in front of p}. Superior molars 
bunoselenodont with an oblique ectoloph, including a very prominent 
parastyle and sharply defined mesostyle; protoloph with a sharply 
defined protoconule. Manus with the fourth digit reduced, functionally 
tridactyl with lunar widely displaced. 
L. popoacicus Cope.’ This species was established upon two man- 
dibular rami with the anterior and posterior portions fractured (Am. 
Mus. Cope Coll., 4863). The animal is small (pm2—m3=.069), rang- 
ing in size between the largest Hyracotheres and smallest species of 
Paleosyops (P. brownianus). Remains of twenty individuals are — 
now contained in the American Museum, Cope Collection. The num- 
ber of incisors is unknown and it is also uncertain whether there are 
three or four premolars. The incisors are chisel-shaped. The canines 
are sharply pointed. The second and third upper premolars have — 
single internal lobes. The form of the molars is very characteristic; 
they differ from the contemporary Hyrachothere molars in the obliquity 
of the ectoloph, the prominent parastyle and sharply defined meso- 
style, the protoconule is acutely triangular, while the metaconule is 
not defined but merged in the low metaloph ; in fact, the inner half of 
the crown is quite like that of the early horses. In the lower jaw P, 
is a laterally compressed protocone, P, has rudiments of additional 
cusps, P, is submolariform with its tetartocone rudimentary or absent. 
The lambdoidal lower molar crests give the name to the genus; the 
the paraconid (as in the Hyracothere) is feebly reduplicate; in M; 
the hypoconulid varies from a conic to a selenoid or crested form. 
The few skeletal characters known are very significant (See Am. Mus., 
Cope Coll., No. 4880). Asin the Equide the vertebrarterial canal 
passes through the upper side of the transversal process of the atlas. 
The displacement in the manus is extreme, the lunar resting on the 
unciform and demonstrating that although four toes existed the foot 
was mesaxonic ; at the same time the median digit was not greatly en- 
separated inferior and sustentacular facets as in the horses. 
Remains of the tibia, of the calcaneum and other characteristic 
limb bones all resemble the corresponding parts in the contemporary 
Equide. 
1 Am. Nat., 1880, p. 748, Tert. Vert., p. 
