1014 The American Naturalist. [December, 
conule and:suggesting an incipient protoloph. The selenoid 
external cusps of this type suggest a comparison with the 
lopho-selenodont perissodactyls, and we are able to reach the 
following result. 
In a large series of Coryphodon molars we see first that the 
protoloph is formed of the protocone, protoconule and para- 
style, exactly as in the horses. Unlike the horse (Anchither- 
ium), the ectoloph is more or less detached from the protoloph, 
but the examination of a large series of specimens in the 
American Museum and Cope’s collection convince us that it is 
composed of the same elements as in Anchitherium, namely, 
the paracone, which has almost lost its crescentic form, the 
mesostyle, which is much less prominent, and the metacone, 
which is still crescentic. This enables us to describe this 
molar as follows: It is of buno-selenodont origin and has a 
complete protoloph and ectoloph, but no metaloph. Its homo- 
logies with the elements of the Anchitherium molar are clearly 
shown by a comparison of Fig. 12 and Fig. 15. This illus- 
trates again the necessity of starting upon the trigonal basis 
instead of upon the basis of two lobes, as in the work of French 
paleontologists. In his“ Enchainements du Monde Animal,” 
Prof. Gaudry has admirably worked out the upper molars of 
the perissodactyla and artiodactyla from the sexitubercular 
stage onwards. He divides the tooth into two lobes, a “ pre- 
mier lobe,” including our protocone, protoconule and paracone 
and a “second lobe” including our hypocone, metaconule and 
metacone. All subsequent authors in France follow this sys- 
tem, which indeed works well for one group. But what we 
need now is a system which will apply not only to all groups 
of ungulates, but to unguiculates as well, so that when we 
reach the upper Cretaceous borderland between unguiculates 
and ungulates we can employ the same set of terms and the 
same basis of description. 
I can only conclude by expressing the conviction that the 
tritubercular theory of Cope rests upon such conclusive evi- 
dence that its universal adoption as the key to the interpreta- 
tion of all molar teeth cannot be long deferred. It is one of 
the chief anatomical generalizations of the present century. 
