1897] NOTES AND COMMENTS 151 
For many years there have been known more or less imperfect 
remains of certain remarkable and puzzling mammals from the 
Eocene of the United States, which have been described under the 
names of Hemiganus, Psittacotheriwm, Calamodon, and Stylinodon ; 
the two first being from the Puerco beds, while the third is from 
the Wasatch, and the fourth from the Bridger and Wind river. 
The unfortunate animals to which these bones and teeth belonged 
have been shifted about from place to place, according to the fancy 
or bias of each individual describer; one of their last resting- 
places being among the Tillodontia. 
Dr Wortman has, however, succeeded in showing that whereas 
in the latter it is the second incisor in each jaw which (as in the 
rodents) undergoes hypertrophism, in the animals forming the 
subject of his memoir it is the canine which undergoes special 
enlargement. Obviously, therefore, there can be no intimate re- 
lationship between the two groups; and as the one he has specially 
investigated requires a new title, the name Ganodonta has been 
proposed. 
To enter into details of the structure of these ganodonts would 
obviously be out of place here. But any competent anatomist who 
may take the trouble to consult the excellent descriptions and 
figures given in the original memoir can scarcely fail to be con- 
vinced that in these animals Dr Wortman has succeeded in 
identifying the long-missing ancestors of the American edentates. 
Although the Puerco forms have enamelled and rootless molars, in 
the latter types the roots at first become confluent, and finally 
disappear, while at the same time the enamel becomes restricted 
to bands, and the whole structure of the tooth is simplified. 
The canines, too, become more and more like those of the Pliocene 
and Pleistocene ground-sloths; while the resemblance between the 
skulls and limbs of the latter and these of the ganodonts is such 
as to render no other conclusion possible but that the one group is 
the forerunner of the other. Not only, therefore, have the ancestors 
of the true edentates been discovered, but we have proof that the 
first tooth of the modern sloths is a canine, and not a premolar. 
The Ganodonta are regarded as forming a sub-order of the 
Edentata; the genera mentioned above constituting one family 
(Stylinodontidae), while a second family (Conoryctidae) is made up 
of the genera Conoryctes and Onychodectes, to which further allusion 
is unnecessary in this place. Whether the living Old World 
families (Orycteropodidae and Manidae) should or should not be 
included in the Edentata, Dr Wortman leaves an open question ; 
but in either event he confesses himself unable to draw up a 
satisfactory definition of the order, 
