84 Bulletin American Museum of Natural History. [Vol. XXXIV, 
Tritemnodon whitie (Cope 1882). 
Stypolophus strenuus Corr 1881, Bull. Hayd. Sur. No. VI, p. 192 (not S. strenuus 
Cope 1874); S. whitie Corr 1882, Proc. Am. Phil. Soc., Vol. XX, p. 161; Tertiary 
Vertebrata, p. 292, pl. xxvb, figs. 8-14. 
Distinctive characters: M,_3 = 22.5; molars compressed, with small heels, enamel 
smooth; no metacone on m’; small inner heel on p’. 
Type, A. M. No. 4781 lower jaw and part of skeleton from the Lost Cabin horizon 
of the Wind River Basin. 
A partial skull and lower jaws No. 4782 from the same horizon and 
locality has been fully described and figured by Cope. I have seen no 
additional specimens positively referable. It is approximately intermediate 
in tooth characters between S. hzans of the Lysite and 7. agilis of the Lower 
Bridger, although smaller in size than either. 
MESONYCHIDE. 
This family is typically represented in the Lower Eocene by the genus 
Pachyena which includes a number of larger and smaller species, and is 
fairly common. The Paleocene genus Dissacus also survives into the Gray 
Bull horizon, and the peculiar little Hapalodectes occurs in the Lysite and 
Lost Cabin levels. | 
In discussing the Bridger Mesonychide in 1909, the writer pointed out 
their aberrant character among Creodonta and resemblances to Artio- 
dactyla which ought not to be hastily attributed to parallelism. This 
and other considerations have led Dr. Gregory to view the Artiodactyls as 
derivatives of some ancient Creodonta near the Mesonychide. The skele- 
ton characters of Dissacus and Pachyena do not however, lend much sup- 
port to the argument for this view. Pachyena shows the artiodactyloid 
characters in a diminished degree, Dzssacus still less. The skeleton of 
Trusodon is hardly known, but there is a very considerable gap between it and 
Dissacus in the construction of the teeth — partly bridged by M¢croclenodon. 
If all these genera are to be included in the one family, it must be regarded 
as one of very ancient differentiation, but its abnormal characters (for a 
Creodont) appear to be all adaptive to some peculiar mode of life. 
I may repeat that the alleged carrion-eating habits! are not at all indi- 
1 Scott, 1913, Land Mammals of the Western Hemisphere, pp. 560-561. Exception 
must also be taken to Professor Scott’s statements that Pachyena ‘“ retained the epicondylar 
foramen of the humerus and pentadactyl feet’’ and that Dissacus had sharp claws. It is 
also doubtful whether the typical species of Dissacus had five functional digits. 
