VII 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. SS. 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 lke that of Psittacotherium. 
Tn 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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