480 THE MAMMALIA OF THE UIISTTA FORMATION. 



more .complicated than its predecessoi's ; it consists of a high, acute, and compressed 

 cone with a small and sharp antero-internal tubercle ; from the inner side of the apex 

 of the principal cusp there runs downwards and backwards a thin ridge, which en- 

 closes a very narrow valley between itself and the outer posterior edge of the crown. 

 The corresponding tooth in Tracjulus has quite a ditferent appearance. 



The molars are very brachyodont and are rather short in the antcro-posterior 

 direction ; the inner cusps are conical and thick, not flattened out into thin plates ; 

 the outer crescents are somewhat trihedral in section and rather angular than curved. 

 The valleys are widely open at the top, but rapidly narrow below, becoming 

 mere slits after a moderate degree of attrition. The two valleys of the same tooth 

 are not quite connected, being separated by the deep constriction between the two 

 outer crescents and by the coalescence of the posterior turn of the anterior crescent 

 with the inner wall of the tooth. They are, however, closely adjacent and even in an 

 advanced stage of wear do not become widely separated. The cingulum is quite 

 sti-ongly marked upon the anterior and posterior faces of the crown, as well as be- 

 tween the outer crescents, where it foi'ms a distinct accessory column, which is largest 

 on the first molar. The heel of the last molar is relatively large and encloses a broad 

 valley ; a narrow cleft appears upon its inner wall. 



The teeth associated with the skeletal fragments about to be described are so 

 much damaged that their reference to this genus is not quite certain, though very 

 probable ; they are somewhat larger than those of the type specimen, and may, per- 

 haps, represent a second species. 



Vertehrce. An isolated atlas is probably to be referred to this genus. It just 

 reverses the proportions of the atlas of Protoreodon in being long and narrow, and 

 with but slightly extended transverse processes ; between the anterior and posterior 

 articular surfaces the body of the vertebra is deeply constricted. The anterior co- 

 tylus for the occipital condyle is very deep and transversely extended, narrow from 

 above downwards, and is slightly notched on the outer edge. The transverse p)"0- 

 cesses are thin plates and do not appear to be perforated at the base by the verte- 

 brarterial canal. The surfaces for the centrum of the axis are flat, oval and placed 

 almost transversely ; there is no facet upon the posterior edge of the inferior arch of 

 the atlas, for the centrum of the axis beneath the odontoid process, such as occurs in 

 the camels and true ruminants. Fragments of other vertebrai occur in the collec- 

 tion, which undoubtedly belong to Leptutragidu^, but they arc not sufficiently well 

 preserved to warrant desci-ii)tion. 



Of the scapula, the distal portion is preserved. The glenoid cavity is oval in 

 shape, the antero-postcrior diameter exceeding the transverse ; the coracoid is promi- 



