70 ON THE EXTINCT MAMMALIA OF 



URSIDJS. 

 LEPTARCTUS. 



Leptarctus primus. 



A small carnivorous animal, distinguished by the above name, suspected to be 

 allied to the existing genus Nasua, is inferred to have existed from an isolated tooth, 

 found ]jy Dr. Hayden in association with remains of Merijchippus and Eipparion, at 

 Bijou Hill, east of the Missouri River, about ten miles below the mouth of White 

 River, Dakota. 



The specimen, represented in figures 15, 16, plate I, one and a half times the 

 diameter of nature, is a left superior molar tooth, nearly resembling in size and con- 

 struction the fourth upper molar of the Coati, of South America. 



As in the latter animal, the tooth has a trihedral crown, and three fangs holding 

 the same relative position. 



The crown has nearly the same proportions as in the Coati, but is rather longer in 

 relation Avith its other measurements. As in the Coati, it is constituted of three 

 tubercles externally and two internally. In the fossil the median outer tubercle or 

 cusp is the largest of the five. The joostero-external tubercle is proportionately longer 

 than in the Coati. The summits of the median and postero-external tubercles are 

 continuous, through a trenchant curved edge. The antero-external tubercle is rather 

 less well-developed than in the Coati, and is not conical, but crescentoid, with an acute 

 edge or summit continuous with the bases of the median-external and the antero- 

 internal tubercle. The latter is smaller than in the Coati, and is rather trihedral than 

 conical, while the postero-intefnal tubercle is proportionately larger, so that the 

 internal tubercles in the fossil are comparatively small and nearly equal in size, 

 whereas in the Coati the antero-internal tubercle is not only much longer than the 

 one behind, but is nearly or quite equal to the median external tubercle. 



The measurements of the specimen, in comparison with those of the corresponding 

 tooth of the Coati, are as follows : 



Fourth superior molar. Leptarctus. Coati. 



Antero-posterior diameter of crown, 



Transverse " " ... 



Length of crown, ...... 



