OF THE MESOZOIC MAMMALIA. 
213 
Therefore, selecting the tubercular character of the molars as a common character, we 
may adopt for this group, with a modified definition, the Marsupial sub-order 
Multituherculata which has been proposed by Professor Coped The second group is 
characterized negatively by its wide separation from the first, rather than by the 
presence of distinctive characters common to all its members, and for reasons Avhich 
will be fully stated later, it does not appear to constitute a single well defined division. 
The first group is much more primitive than the second ; it was apparently widely 
spread in the upper Triassic and extended upwards, while the second group, with the 
exception of two genera which are very distantly related to the others, appeared in the 
lower Triassic, and was widely distributed in the upper Jurassic. 
Figures. The molar tooth forms of the multituberculate marsupials. 1. Triglyphus, an upper molar 
la, ditto, in side view, natural size. 2, 2a. Tntylodon, an upper molar, wearing surface and outside view 
natural size. 3. Polymastodon, the second upper molar, natural size. 4. Bolodon, the third and fourth upper 
molars, enlarged about 6 diameters. 5. Slereognathus, a lower molar enlarged about 2J diameters. 6. Chirox, 
the upper molars enlarged 1 J diameters. 
A. FIRST GROUP 
SUB-ORDER MULTITUBERCULATA.— Cope. 
An extinct sub-order of Marsupials in which the teeth are below the typical 
number ; one incisor on each side is greatly developed ; the lower canines are 
rudimentary or wanting; there is a broad diastema in front of the premolars and the 
molars are provided with tubercles in two or three rows with longitudinal valleys 
between them. Th( 
1. Plagiaulacidse 
A single lower incisor. 
Premolars in both jaws 
developed into flat cut- 
ting blades. Lower mo- 
lars with irregular tuber- 
cles ; in early forms a 
vertical ; in later forms a 
fore-and-aft grinding mo- 
tion between the molars. 
(Upper molars with three 
parallel rows of tub- 
ercles.) 
1 “ Tertiary Marsupialia,” American Naturalist, 1884, p. 681. The order AUotheria was proposed by Pro- 
fessor Marsh (Am. Journ. Sc. and Arts, Sept., 1880), to embrace Plagiaulax and Ctenacodon and other genera, 
but without the statement of characters suflicient to distinguish it from the Marsupialia. 
!re is no mylohyoid groove in the mandible. 
3. Tritylodontidx 
2. Bolodontidx 
Two or three upper in- 
cisors. Upper premolars 
tubercular. Upper mo- 
lars with two regular rows 
of conical tubercles, adap- 
ted toafore-and-aftgrind- 
ing motion, separated by 
longitudinal grooves or 
valleys. 
Two upper incisors. 
Upper premolars tuber- 
cular. Upper molars 
with three parallel rows 
of conical tubercles, ad- 
apted to a fore-and-aft 
motion, separated by 
longitudinal grooves. 
4. Polymastodontidx 
A single lower incisor. 
One simple premolar in 
the lower jaw, no upper 
premolars. Two molars 
in each jaw. Three rows 
ofpavement tubercleson 
upper molars, two rows 
on lower molars, adapted 
to a fore-and-aft motion, 
without wearing grooves. 
