796 The Condylarthra. [ August, l 
the loss of a premolar. The only species, Hexodon molestus, is 
known from the superior and inferior dentitions of a single indi- 
vidual. It differs from the Æ, ditrigonus in the short, rounded inci- 
sive region and closely-placed incisor teeth, the small posterior 
superior molar, and the more robust and more vertical canine 
teeth (Fig. 5). It is about the size of the red fox, but much more 
robust. It is one of the few species of the family which is armed 
with large canine teeth, and evidently stood preéminent in its 
powers of offence and defence. In the typical specimen the teeth 
are all worn by the mastication of hard or tough substances, s0 
that the structure of the crowns of the true molars is not entirely ; 
known. 
In-Ectoconus Cope, we have the most complex structure of — 
the molars in the family, or that the tritubercular type of supe- 
rior molar is known to present. There are eight cusps on each 
crown, viz., one external cingular; two external; two interme- 
diate ; one internal; two (anterior and posterior) interior cingular. 
The typical species is the Æ. ditrigonus Cope, an animal about the 
size of the collared peccary. Its upper lip, and probably muzzle, 
are prominent, since the premaxillary bone is produced, an the 
small conic incisor teeth are widely spaced (Figs. 4-5): The 
limbs were robust, and had the general character of those of 
Periptychus. Thus the astragalus is flat, and the humeral con- 
dyles are wide, and resemble those of a carnivorous animal. 
Several individuals have been obtained by Mr. David Bete 
In the genus Periptychus Cope, we have the largest and n 
specialized forms of the family. The molars only differ from 
Se e a o E i 
those of Ectoconus in the entire absence of the external cingu 
cusps (Figs. 1-2). The two genera agree in possessing is a 
cingular lobes of the superior premolars. The inferior premo 
of Periptychus are a little more complex than in the other sn 
era. The canine and incisor teeth are relatively small. Pie 
further characterizes the species of this genus is the extraor : 
sculpture of the teeth of the entire molar series. This ae 
of strong grooves separated by convex ribs, which extend *™ 
the base towards and to the apex of the crown, the num 
Pos to the Con’ 
1 This species is represented by a specimen which is referred by y urvey of the 
nyctes comma, in the Vol. 111 of the Report of the U. S. Geo ech came. Bettet 
Terrs.,p. , and are represented in Figs. 1-5. Plate XXIII of 
specimens of the C. comma show that the canine (or ? incisor) tee 
ferent character from those of this animal. 
h are of 907% 
ESTEE: aN T LEE SNAS BA HES lg AE a PRE rae NE DD Fe To RTO I SES ee EPIR ER 
