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 Hcmiganus, Psittacotherinm , 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 

 (Stylinodontidac), while a second family (Conorydidae) is made up 

 of the genera Conorydcs and Onychodectcs, to which further allusion 

 is unnecessary in this place. Whether the living Old World 

 families (Orycteropodidae and Manidae) should or should not be 

 included 4n 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. 



