272 0. C. Marsh — Description of Tertiary Artiodactyles. 



A specimen in the Tale Museum representing a different 

 species, apparently pertains to the same genus, and proves, 

 moreover, that the original suggestion as to the nature of the 

 animal was probably correct. This specimen is in fine preser- 

 vation, and consists of the skull and greater portion of the 

 skeleton of an adult individual about as large as a rabbit. One 

 interesting feature of the skull is the comparatively large size 

 of the brain cavity, and the cast it contains shows well-marked 

 convolutions. The dentition is of special interest. The upper 

 molars resemble those of Helo/iyus, especially the last molar of 

 that genus. They have each two outer cones, a single large 

 inner cusp, and two intermediate lobes, the anterior uniting 

 by wear with the inner cusp so as to form a crest. The fourth 

 premolar has a single outer cone and one inner cusp. The 

 third premolar is very large, and subtriangular in outline. The 

 second premolar is secant, and behind it is a well-marked 

 diastema. The teeth are shown in figures 29 and 30 below. 



29. 



30. 



Figure 29. — Upper teeth of Leptochcerus gracilis, Marsh : 

 Figure 30. — Lower teeth of the same skull ; top view. 

 Both figures are twice natural size. 



seen from below. 



The lower jaws in the present species are slender, especially 

 in front. The lower molars are very small, decreasing in size 

 to the last. The fourth premolar is larger than the first molar. 

 The anterior premolars are secant, and there is a diastema in 

 front and behind the second. There is a deep groove on the 

 inner side of the lower jaw, extending from the dental foramen 

 nearly to the symphysis. 



The radius and ulna are separate, and the latter well devel- 

 oped. There were apparently four functional digits in the 

 manus. The fibula is much reduced. Its lower portion has 

 coalesced with the tibia. The hind foot resembles that of 

 Homacodon, having four usable digits, but the navicular and 

 cuboid are coossified, an unexpected feature. 



