128 ON THE EXTINCT MAMMALIA OF 



The auditory bulla) are equally huge with those of Z. major in proportion to the 

 size of the species. They form oval capsules, ten and a half lines fore and aft, seven 

 and a half lines wide, and seven lines deep. 



The lower jaw has the general construction and form of that of Oreodon, but it is 

 proportionately short at its fore part in relation with the shortness of the upper jaw, 

 and its posterior part is of much greater proportionate depth. Indeed, the dispropor- 

 tion between the back and front portions is so great as to remind one of the condition 

 of the lower jaw in the Howling Monkeys. 



The coronoid process is proportionately shorter and broader than in Oreodon. The 

 fossa below is rather deeper. The base, as partially seen, below the position of the 

 molars is rapidly ascending forward. 



The molar teeth oi Leptauchenia decora, as exhibited in the specimen of the skull 

 from which the above description is given, and in a number of additional fragments 

 of jaws, figures 6 — 20, are like those of the larger species L. major. 



Figures 7 — 10, plate XII, represent two fragments, apparently from the same 

 upper jaw, the one containing the last two true molars, the other the last three pre- 

 molars. 



The true molars, figures 7, 8, are moderately worn; the last had not entirely 

 protruded, and the triturating surface had not been sufficiently worn to expose a 

 continuous tract of dentine throughout all its lobes. 



In the second molar, figure 8, the exposed dentine is continuous on the summits of 

 all the lobes, and encloses a median pair of bent vertical plates of enamel belonging 

 to the inner faces of the outer lobes. The exposed dentine of the inner lobes, 

 approaching the bottom of the plates just indicated, appears to be separated from 

 them only by a narrow fissure, without perceptible enamel bounding the inner face of 

 the latter. 



In the last molar, figure 8, the exposed dentine of the summits of the anterior pair 

 of lobes includes a narrow crescentoid enamel pit, bounded externally by a compara- 

 tively deep wall consisting of the inner enamel layer of the antero-external lobe. A 

 narrow tract of dentine is exposed, from attrition, on the fore part of the summit of 

 the postero-external lobe of the same tooth, and is continuous with the exposed 

 dentine of the anterior pair of lobes. The outer inclined face of the postero-internal 

 lobe, when closely examined, appears unworn, and yet its dentine appears to be 

 exposed. The enamel on the exterior of this lobe appears to cease with its triturating 

 border. The apparently unenamelled surface of the postero-intei'nal lobe is continu- 

 ous with a similar patch on the postero-internal surface of the postero-external lobe. 



The premolars, figures 9, 10, agree Avith those of Z. major, except that the central 

 enamel pit of the last of the series is more open, as in Merycliyus elegans. 



The lower molars, represented in figures 13 — 20, agree closely with those ofi. 



