ON SOME NE^Y AND LITTLE KNOWN CREODO.NTS. 
169 
compressed and backwardly directed cone, and the posterior is a much lower trenchant 
heel, convex externally and concave internally. The attrition takes place on the sum- 
mits and not on the sides of the lobes, so that they become more and more blunt with 
age. The ordinal arrangement of these teeth cannot be certainly determined, as they 
are all detached, but judging front the amount of wear, the first is the largest and the 
third the smallest, though there is much less difference in this respect than in the other 
species of the genus. The anterior basal tubercle is small on the first, still more 
reduced on the second and entirely absent from the third. This reduction gives the 
molars a somewhat different appearance from that seen in the species from the Bridger. 
The mandibular condyle differs in no respect except size from that of the other species. 
I have referred this animal to Mesmyoc, because the parts preserved do not show 
any differences of generic value. But in view of the character of the incisor and pre- 
molar teeth, it is quite j)robable that more perfect specimens wdll necessitate the form- 
ation of a new genus for its reception. At all events it certainly is a member of the 
MesonycfiidcB and w^ould seem to be the last variation which occurred before the extinc- 
tion of this peculiar type. 
Measurements. 
M. 
Diameter of incisor (fore and aft) . . .011 
“ “ (transverse) . . .011 
Length of lower premolar (1st 1) . . .014 
“ “ “ (2nd1) . . .018 
Length 1st lower molar . . .• . .031 
Thickness “ “ . . . . .015 
Length 2nd “ . . . . .029 
Thickness 2nd “ . . . . .015 
Length 3rd “ . . . . .028 
Thickness 3rd “ . . . . .012 
Transverse diameter mandibular condyle . .037 
Genus DIDYMICTIS. 
III. Didymictis altidens, Cope. 
The MiacidcE approach nearer to the true carnivores than do any other creodonts. 
and consequently even very imperfect specimens are worthy of careful description. 
A fragmentary skeleton of Didymictis altidens obtained by the Princeton Expedition 
of 1884 in the Big-Horn basin of Wyoming (Wasatch formation) will serve to shed 
some additional light upon the characteristics of this flunily. 
With regard to the dentition I can add nothing to Professor’s Cope’s account 
except to say that lower incisors were very probably present, as is shown by a loose 
tooth occurring with this specimen ; it is very small and has a simple crown and strongly 
curved fang, but no cingulum. The number of lower incisors cannot be made out, 
but as the space between the approximated canines is much reduced, it seems probable 
that not more than two were present in each ramus. 
