THE OSTEOLOGY OF HYiENODON. 
499 
THE OSTEOLOGY OF HY^ENODON. 
By W. B. Scott. 
(Investigation aided by a grant from the Elizabeth Thompson Fund of the A. A. A. S.) 
In a paper published in the Journal of the Academy of Natural Sciences of 
Philadelphia in 188 i (No. 6) I gave an account of the osteology of this genus so 
far as the materials then available would permit, but those materials were very 
imperfect and left much room for conjecture. The Princeton Expedition of 1894 
was especially fortumite in collecting specimens of Hycenodon, Mr. Hatcher having 
found several more or less complete skeletons representing a number of different 
species. I am no\v in a position, therefore, to supplement the earlier account and 
to give a restoration of the skeleton of this very curious and remarkable animal. 
For the sake of completeness a description of the parts of the skeleton already 
known is added to those wdiich are here described for the first time. The rapid 
increase in our knowledge of the creodonts which has taken place in the last seven 
years makes it necessary' to go over this ground again from a somewhat different 
point of view, in order to make clear the systematic relationships of the genus. 
No less than six species of Hycenodon have been identified in the White River 
or Oligocene beds. These may be conveniently arranged as below. This tabular 
carrangement, however, is not intended to express the mutual relations of the species. 
I. Upper premolars three, H. pauadens 0. . 
II. Upper premolars four. 
A. Palatines in contact throughout; pterygoid ‘i 
plates of alisphenoids meeting below, H. leptocephalus Scott 
B. Posterior nares between palatines, pterygoid plates separate. 
a Postorbital constriction in advance of 
fronto-parietal suture, H. cr^uians Leidy 
b. Postorbital constriction at or behind fronto-parietal suture. 
1 Size very' large ; frontal sinuses much 
inflated, P2 with posterior cusp, H. horridus Leidy 
2 Size moderate; sinuses less inflated, 
P2 without talon, H. cruentus 
3. Size minimal, P-” = 58 mm., H. m^istehnus sp. nov. 
HY.*:NOr>ON MUSTELINCS sp. UOV. 
This species is characterized by its small size, 
known, the uniform size of the upper premolars 
6.5 JOUEN. A. N. S. PHILA., VOL. IX. 
less than that of any other yet 
(except F), the acuteness of the 
