190 BULLETIN UNITED STATES GEOLOGICAL SURVEY. [TolYl. 



According to Leidy's measurements, tlds species is about the size of 

 Ms M. vorax of the Bridger formation. That species has, like the two 

 others of that horizon, a second tubercular tooth with only one root. 



Measurements. 



M. 



Length, of dental line posterior to canines 0440 



Length of premolar series 0250 



Length of base of fourth premolar 0065 



Length of base of sectorial 0085 



Length of base of first tubercular 0060 



Length of base of second tubercular 0040 



Depth of ramus at second premolar 0150 



Depth of ramus at second true molar 0100 



This species was probably about the size of the gray fox. 



23. MlACIS BREVIROSTRTS Sp. nOV. 



This species differs from those of the Bridger epoch in the same way 

 that M. canavus does, i. e., in the biadicate last inferior molar. Its dimen- 

 sions are intermediate between those of 31. edax and M. vorax, hence a 

 little smaller than those of the M. canavus. This difference is partially 

 seen in the shortening of the premolar series of teeth. They are closer 

 together than in the 31. canavns, and the roots are larger. The sec- 

 torial tooth is shorter. The fourth premolar has a low anterior basal 

 cingulum ; the posterior part of the crown is robust. The first tuber- 

 cular molar is wide, and consists of a basin-shajied heel and a short 

 anterior portion which is more elevated. The latter consists of two 

 cusps, which are connected by an anteriorly convex ledge, but there is no 

 third anterior tubercle as in 31. parvivorus. The ramus is quite robust, 

 and the basis of the canine tooth is unusually large. Mental foramina 

 are below the anterior parts of the second and fourth premolars, respect- 

 ively. Last inferior molar small. 



3feasurements. 



• . . • M. 



Length of molar series 0380 



Length of premolars 0200 



Length of base of fourth premolar 0060 



Length of base of sectorial 0072 



Length of base of first tubercular 0048 



Length of base of second tubercular 0042 



Depth of ramus at second premolar 0140 



Depth of ramus at second true molar 0140 



24. DiDYMICTIS ALTIDENS CopC. 



American Naturalist, 1880, Oct. p. 746. 



Eepresented by several specimens. The species is larger than the 



D. protenus, or about equal to the coyote ; but the tubercular molar is 



relatively smaller, and has the three anterior cusps better developed. 



The heel of the tubercular sectorial is longer and the three cusps more 



