STYLINODON 193 



are double-ridged, and that transversely to the long axis of the 

 jaw; finally, the much-worn teeth have flattish crowns more or 

 less surrounded by a ring of enamel. 



A still later form, coming from the Lower and Middle Eocene 

 strata, is the genus Stylinodon. S. cylindrifer, which is the more 

 archaic of the two described species, is only known from a single 

 molar, fragments of a canine, and " some inconsiderable pieces of 

 the skull." The molar is interesting on account of the fact that 

 the enamel is still further reduced ; it is represented only by 

 narrow vertical strips, which are much narrower than those of 

 older forms of Ganodonts. It is also hypselodont, and has a 

 persistent pulp. So, too, the canine which had a thick anterior 

 facing of enamel. The later species, S. mirus, is more fully 

 known. The teeth seem to have been much the same as in the 

 last-described species ; the premolars and molars were seven in all 

 in the lower jaw, and the canine was imbedded in the bone for a 

 long distance, as in Calamodon. The cervical vertebrae have 

 short centra as in Hemiganus. The clavicles were well developed. 

 The humerus possessed an entepicondylar foramen, and its head 

 displays the pyriform pattern so characteristic of later Edentates. 

 The foot is clearly like that of Psittacoiheriwn. 



In reviewing the series, therefore, we see a gradual diminution 

 of the incisors, a gradual loss of enamel on the teeth generally, 

 and the production of hypselodont teeth growing from per- 

 sistent pulps ; all of which are features of the later Edentates. 

 The progression is so gradual that the forms enumerated and 

 described seem to have been part of a continuous series cul- 

 minating in the Ground Sloths of later times. The other points 

 of similarity will be gathered from the facts given in the fore- 

 going pages. 



There is another family belonging to the Ganodonta whose 

 position with regard to the Edentata is not so clear. This is 

 the family Conoryctidae, of which two genera are known. The 

 earliest of these, from the Lower Puerco, is Onychodectes. In 

 0. tissonensis the skull is long and narrow, thus contrasting with 

 that of the last family. The facial part is also long. The lower 

 jaw is much more slender. The molar formula was complete, 

 but there is some doubt as to the incisors. The molars are 

 tritubercular. 



The other known genus is Conoryctes. Its skull has a shorter 



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