Cope. | 546 (Jan, 18, 
LEPTAUCHENTA Leidy. 
Extinct Mammalia of Dakota and Nebraska, 1869, 122. Proceedings 
Academy Philad’a, 1856, 88, (nomen nudum), loc. cit. 1656, 163 (nomen 
nudum), 
As already remarked by Leidy, this genus is characterized by the pres- 
ence of enormous vacuities of the superior surface of the muzzle. The 
genus might be described as lacking the usual superior osseous wall of the 
nasal cavities and maxillary sinuses, The generic diagnosis is as follows: 
Otic bulle inflated. Four premaxillary teeth. Nasal bones excessively 
contracted, leaving a wide interspace between them and the maxillaries. 
Symphysis mandibuli codéssified. 
This genus has but a short range in time, not having been yet found out 
of the Ticholepttis beds. It shows in its deficient ossification, and smaller 
size, that this line of the family was approaching its extinction, its deca- 
dence having already commenced in the genus Merychyus. The genera 
which follow in systematic order, Cyclopidius and Pithecestes, exhibit the 
last steps in the downward course, 
I. Infraorbital foramen above P-m. iii. 
“Three inferior incisors; nagal sinuses to middle of orbit ; 
true molars .048 s skull 186.’ Cheldyy iis evince sed evuldl MOTT. 
‘Nasal sinuses not extending so far posteriorly as in L. major ; 
true molars Obes eleull; 101,’ CLeldy ie svi dee owe 6 
‘‘Nasal sinuses reaching to front of orbit; true molars .020 ; 
BR O80. CGT yes viv vet CUS sie We ere Wie Cini wlhy he soerdn nitida, 
» Gecona. 
Leptauchenia major Leidy. 
Proceedings Academy Philad’a, 1856, p. 163; 1857, 89. Extinct Mam- 
malia, Dakota and Nebraska, 1869, p. 124, Pl. XII, figs. 1-5. 
Tributaries of White river, Nebraska, 
Leptauchenia decora Leidy. 
Proceedings Academy Philadelphia, 1858, p. 88; 1857, p. 89. Extinct 
Mammalia of Dakota and Nebraska, 1869, p. 127, Pl. XII, figs. 6-20. 
Tributaries of White river, Nebraska. 
Leptauchenia nitida Leidy. 
Extinct Mammalia of Dakota and Nebraska, 1869, p. 129; Pl. XII, figs. 
21-22, 
White Earth creek, Dakota, tributary of the White river. 
IWCLOPIDIUS Cope. 
Proceedings American Philosophical Society, 1877, p. 221. Brachy- 
meryx Cope, Ibidem, p. 220. 
Dental formula: I. 9; C.+; P-m. $; M. % Premaxillary bones much 
reduced ; mandibular rami coéssified. Otic bulla inflated. Prelachrymal 
vacuities present, and confluent with enormous nagal vacuities, which are 
due to the excessive reduction of the nasal bones. Orbit closed behind. 
