1896.] NATURAL SCIENCES OF PHILADELPHIA. 385 



formidable of its genus, and it probably found an abundant supply 

 of food in the sloths of the genus Megalonyx, which were the most 

 abundant of the contemporary mammalia. 



Osmotherium spelaeum Cope. 



This genus is characterized by inferior dentition as in Mephitis, 

 but the dental formula Pm. 4, M. 2. Metaconid well developed ; 

 heel of sectorial large, cupped. 



The inferior dental formula of this genus is that of the extinct 

 form, Potamotherium, which intervenes between Mephitis and 

 Lutra. The typical species of Osvxotherium, however, resembles 

 Mephitis so greatly in its inferior dentition that I suspect that the 

 superior molar formula will be found to be Pm. 3, M. 2, as in Me- 

 phitis, instead of Pm. 4, M. 2, as in Potamotherium. The latter 

 genus is of the Miocene age in Europe and North America, the 

 genus Brachypsalis Cope from the Loup Fork formation of Ne- 

 braska being probably founded on a species of Potamotherium, 

 The presence of an additional premolar is important in the Musteli- 

 dse, but might in some case prove to be a mere individual variation, 

 but in the present instance this is clearly not the case. 



Osmotherium spelaeum Cope is represented by a left mandibular 

 ramus which contains alveoli or roots of the C. and Pm. 4-2, with 

 Pm. 1 and Ms. 1-2 perfectly preserved. 



The ramus is robust, and its inferior border rises from below the 

 heel of M. 1 upward and posteriorly ; in Mephitis mephitica the 

 ramus is less robust, and the inferior border begins to ascend below 

 the posterior part of the M. II. The anterior border of the mas" 

 seteric fossa is not sharply defined. There are three mental fora- 

 mina, the first and second below Pm. 2, and the third below Pm. 

 1, the anterior being the largest. The molar teeth are much like 

 those of 31. mephitica, but are more robust. The metaconid is 

 considerably smaller than the protoconid as in Mephitis putorius, 

 and smaller than in M. mephitica. The borders of the heel are 

 strongly and equally elevated, enclosing the basin completely. The 

 Pm. I differs from that of 31. mephitica in presenting a flat face 

 inward and posteriorly, which is bounded externally by an angu- 

 lar ridge, as in 31. fossidens. The crown of the Pra. 2 is mostly 

 lost, but a short, flat transverse heel remains, which is similar to 

 but smaller than that of the Pra. I. The anterior root of Pm. II 

 is opposite the posterior root of the Pm. Ill ; while the Pm. IV is en- 

 tirely and directly in front of the anterior root of Pm. II, and ex- 



