OF THE MESOZOIC MAMMALIA. 
227 
character of the molars. This is the Caknivorous series, and may be distinguished 
as follows : the molars have three stout, erect cusps in the same fore-and-aft line, or 
with the lateral pair rotated inwards, without an internal heel but showing an 
internal cingulum. The premolars, when present, have prominent “cingulum” or 
“ basal ” cusps. The canines are erect. The incisors are semi-procumbent to erect. 
The mandible is usually stout, with a broad coronoid process, and in two cases a 
transversely extended condyle on or below the molar level and often on the plane of 
the angle. The most highly specialized genus is Triconodon, in which the incisors, 
canines and premolars are well adapted to a carnivorous diet ; the molar cusps are 
sub-trenchant, the upper being worn sharp by the lower. (Plate VIII, ftg. I). The 
closest modern ally is Th;/lacinus. 
(2) The second, or Omnivorous series, embraces a number of families which are 
closely inter-related both as regards their dentition and probable form of diet. The 
molars are characterized by a more or less complete opposition of cusps upon the 
crown, i. e., the cusps are placed transversely, but do not .show the sectorial disposi- 
tion. In the typical forms, such as Peralestes, tlie upper and lower molars oppose 
eacli other somewhat as in PidelpJii/s, but not with cutting edges. The internal 
cingulum, invariably present in the first sub-group, is here replaced in the lower 
molars by a more or less prominent series of cusps. The posterior basal cusps of the 
premolars, if present, are somewhat less prominent than in the first group ; anterior 
basal cusps are always wanting. The canines are stout, erect and often recurved. 
The condyle is rounded and upon the molar level. The mandible is moderately 
stout and rounded at the symphysis, indicating an erect position of the inci.sors. The 
coronoid is narrower than in the first group. The angle is always separate and well 
defined. 
1. Carnivorous Series. 
1. TKICONODONTID.E,! jpir.^h, 1887. 
The Triconodemtidev. may be defined as follows : Upper and lower molars tcith 
three stout, erect cusps and strong internal cingidtim, not opposed. Opposition of 
dipper and lower molars sub-trenchant. Canines stout and erect, often hifanged. 
Incisors semi-procumbent or erect. Premolars loith prominent basal cusps. Condyle 
low, articidar face sometimes broad. Coronoid process broad. Angle sometimes 
inflected. 
This family embraces numerous genera which are apparently upon divergent 
lines of descent, but are not sufficiently distinct to be placed in three separate 
families, so that we may conveniently, and with more probability of rightly expressing 
their relations, divide them into three sub-families. Amphilestes, from the lower 
Jurassic, is the most central genus, as it has the full complement of teeth and the 
1 “Am. Journ. Sc.,” April, p. 341. 
