PS J TTA CO THERWM I g i 



logical order. The following genera are included by \\"ortnian in 

 his family Stylinodontidae. 



The earliest type of the Ganodonta is the genus Hemiganus, 

 with but one species, H. otariidens. This animal li^'ed during 

 the deposition of the lowest Eocene strata, the Puerco beds of 

 North America. It was about as big as a fair-sized Dog, and had 

 powerful jaws. There were at least two pairs of incisors in the 

 upper jaw, together with powerful canines and the full premolar 

 and molar formula. In the lower jaw the canines were also 

 strong, but the incisors are not certainly known to be more than 

 two pairs. The enamel upon the posterior surface of the canine 

 is thin, and in the case of the incisors the enamel seems to be 

 limited to the anterior face. The lower molars are quadrituber- 

 cular. It is believed from the presence of a sutui-e on the upper 

 surface of the premaxillary that the snout of the creature was 

 tubular. The cervical vertebrae, only known by their centra, are 

 like those of the Armadillos (and for the matter of that of the 

 AVhales) in the great transverse as opposed to the antero-posterior 

 diameter. The feet are especially compared with those of the 

 Ground Sloths. The single ungual phalanx is marked by a large 

 subungual process, which is pierced by a considerable foramen. 

 The tibia again is to be compared with that of the Armadillos. 



In the Upper Puerco (Torrejon) beds the remains of Psitta- 

 cotherium are found. This genus, when first discovered, was 

 referred to the Tillodontia by some and to the Ungulates, the 

 latter being a refuge for indeterminate Eocene mammals, just as 

 the " Multituberculata " is for similarly-placed Secondary mammals. 

 It is now known to be clearly a member of the order Ganodonta. 

 AVortman thinks that there is but one species, P. multifragum. 

 It seems to have had a general aspect much like that of Hemi- 

 f/anus — that is judging from the skull — and was not very greatly 

 different in size. The facial portion of the skull is short, and the 

 zygoma is deep. The infra-orbital canal is double, a feature which 

 crops up in the Sloth, and has been mentioned in the later form of 

 Ground Sloth, Megalonyx (but it must be remembered that the 

 same characteristic is not unknown in Eodents). The dentition 

 is reduced as compared with that of Hemiganus, that is to say, as 

 far as concerns the molars and the incisors. There is but a single 

 pair of incisors in each jaw ; the canines are strong ; the premolar 

 and molar series seem to have been complete in the lower jaw, 



