184 ON SOME NEW AND LITTLE KNOWN CREODONTS. 
Mr M'ortnian* places the -enus among the Inseetivora ; but this I consider to be 
altogOher untenable, as is shown by the convoluted brain, the sectorial dentition, and 
the structure of the vertebr®. 
The origin of the Hycenodoniidce offers a more difficult problem. I was formerly 
inclined to fSlow Professor Cope in deriving them from the Mesomjclddce, but the 
more perfect specimens described in this paper have convinced me that this view is 
erroneous, as the structure of the feet prove, not to mention other characters. The 
evidence now available would seem to point to the Oxycenidce as the family among 
which the ancestors of Hycenodon are to be sought. M. Filhol has shown the close 
relation which exists between Hycenodon and Pterodon ; the latter is distinguished 
by the formula pm. m. |, the presence of internal cusps on the upper molars, the less 
extensive union of the palatines, and by the union of the foramen lacerum posterius 
with the carotid canal. Most of these distinctions are primitive and the only speciali- 
zations which Pterodon shows are .the coalescence of the foramina and the loss of the 
first lower premolar. It seems therefore reasonable to regard the two genera as de- 
scended from a common ancestor very similar to Pterodon. This genus is plainly al- 
lied to Oxymui, indeed Cope includes them in the same family ; between these two 
genera comes P-otopsalis. Oxymna itself cannot be the ancestral genus, on account 
of tlic reduced dentition; but probably some Oxyaena-like form, with full dental series, 
will prove to be the desired ancestral type. 
(The measurements of Hycenodon are included in the same table with those of 
Memnyx.) 
The definition of the group Creodonta is by no means easy, as the order is such a 
large and heterogeneous one. Professor Cope informs me that the only diagnostic 
character which he can find is the involution of the posterior dorsal and lumbar zy- 
gajwphy.ses. A provi,sional definition may be attempted as follows : Unguiculate 
mammals having separate scaphoid and lunar bones in the carpus ; a central bone 
(probably) pi’cscnt in all ; brain small, but in most cases more or less convoluted ; 
molar teeth usually all sectorial or tuberculo-sectorial ; interlocking of posterior dor- 
sjil and lumbar zygapophyses very perfect. 
In conchision I wish to express my thanks to the Academy, and to Professors 
Agassiz and Cope for the loan of valuable material, and to Professor Marsh for allow- 
ing the opportunity to study some of his unique specimens. 
* American System of Dentistry, p. 420. 
