O. C. Marsh—American Jurassic Mammals. 341 
pointed cusps, one, main, outer cone, and two, smaller cusps, one 
in front and one behind, on the inner side. There is a strong » 
cingulum on the inner surface, which may develop into an 
anterior lobe, or posterior heel. The mylohyoid groove is dis- 
tinct. The condyle in Z%nodon.is rounded, and somewhat 
transverse, and is separated from the jaw by a distinct neck. 
In Tinodon bellus, the dental foramen is large (Plate X, 
figure 1, 7), and looks downward and backward. It is placed 
somewhat behind the anterior margin of the coronoid process, 
and somewhat above the middle line of the ramus. The deep 
mylohyoid groove (g) leads from this opening, forward and 
downward. 
Triconodontide. 
Another family related to the one last described is represented 
by the genus Zriconodon of Owen, and by one or two Ameri- 
ean forms. In this group, the premolars are unlike the molars. 
The latter are large, and their crowns are composed of three, 
nearly equal, trenchant cusps. The premolars are compressed 
and trenchant, but lack the anterior cusp. There is apparently 
more than one genus included under the specimens referred by 
Owen to Triconodon, but more specimens will be required to 
separate them. : 
PRIACODON, gen. nov. 
One of the American forms, which appears to be generically 
distinct from the type of Z7iconodon, is represented below, on 
Plate X, figure 9, under the name Przacondon ferow. The 
type specimen, on which it is based, was originally placed 
by the,writer in the genus Z%nodon, and the species named 
Tinodon ferox. Thisspecimen isa right lower jaw, with most 
of the teeth in position. There are three premolars, and four 
molars. The premolars have one main cone, pointed and com- 
pressed, with a low cusp in front, and a larger one behind. 
The last premolar is large. The penultimate molar has four 
distinct cones instead of three. The canine was large, and 
directed well forward. The coronoid process is high, and 
inclined backward. The mylohyoid groove is nearly parallel 
with the lower margin of the jaw, and extends forward to the 
symphysis. The latter is strongly marked. 
Paurodontide. 
A peculiar genus, Pawrodon, widely different from any form 
hitherto found in this country or Europe, is represented at 
present by a single specimen, a left lower jaw. ‘This is shown 
