Mr. E. D. Cope on the Bunothertan Mammalia. 21 
the Tzeniodonta, Tillodonta, Mesodonta, and Creodonta. 
With great apparent diversity, these suborders show unmis- 
takable gradations into each other and the two recent orders 
already mentioned. As such I may mention Psittacotherium, 
which relates the Tzniodonta and illodonta, Hsthonya, 
which relates the Tillodonta with nearly all the other sub- 
orders, Achenodon, which connects Creodonta and Meso- 
donta, and Cynodontomys, which may be Mesodont or Pro- 
simian. ‘Then the existing Chiromys most certainly connects 
Tillodonta and Prosimiz. 
My original definitions of the suborders of the Mesodonta, 
given in vol. il. of the U.S. Geological Survey under Capt. 
G. M. Wheeler, p. 85, omitted the Prosimiz, and embraced a 
number of characters whose significance must be reexamined. 
Thus it is impossible to characterize the Creodonta as lacking 
a trochlear groove of the astragalus, in view of the form of 
that element in Mesonyx and Mioclenus, where the groove 
is more or less distinct. It is impossible to distinguish the 
Insectivora from the Creodonta by the deficiency of canine 
and large development of incisor teeth. In Rhynchocyon the 
canines are large and the superior incisors wanting, while in 
Centetes the arrangement of these teeth is precisely as in the 
Creodonta. As to the large Achewnodon and other Arctocyo- 
nid, I find no characters whatever to distinguish them from 
the generally small Mesodonta. 
In view of these inconsistencies I have reexamined the 
subject, and find the following definitions to be more nearly 
coincident with the natural boundaries of the divisions of this 
large order. ‘The importance of the character of the tritu- 
bercular superior molar has recently impressed me (see ‘ Pro- 
ceedings of the Academy,’ 1883, p. 56), as it had previously 
done Prof. Gill. This zoologist has already distinguished 
two divisions of the Insectivora (without the Galeopithecide) 
by the forms of the superior molar teeth. ‘The first possesses 
quadritubercular molars above, the second tritubercular. 
That these types represent important stages in the develop- 
ment of the molar dentition I have no doubt. These cha- 
racters far outweigh in importance those expressing the forms 
of the skull, matters of proportion only, with which a few 
systematists unnecessarily overload their diagnoses. Such 
characters are of little more than specific value, and serve to 
obseure the mind of the inquirer for a true analysis. ‘They 
may be used empirically, it is true, to determine relationships 
when the diagnostic parts are wanting. 
I propose to transfer the Insectivora with tritubercular 
superior molars to the Creodonta, in spite of the fact that some 
