The Tertiary Marsupialia. 695: 
Tritylodon 
paies RE 
“ Tritomodon” z 
ia t W 
Ctenacodon 
zd Meniscoés sus Plioprion Phascolomys 
Plagiaulax 
| 
Polymastodon Ptilodus Hypsiprymnus 
| . C 
PE à 
Neoplagiaulax Liotomus Macropus 
Thylacoleo 
; It appears from the preceding considerations that the dentition 
of the implacental Mammalia has had a history independent of 
that of the placental series so far as regards the herbivorous 
Ypes at least. I have shown that the primitive types of the pla- 
ntal series were tritubercular, and then quadritubercular, and 
then crested. In the herbivorous marsupials, on the contrary, we 
_Smmence with multitubercular forms, and it is yet an open ques- 
í e saa these have had a quadri- and tritubercular ancestry 
: i Plagiaulacide of the Jurassic period are of very small 
2 “2, none of them exceeding in dimensions the house mouse. 
. same is true of the species of the Eocene period hitherto 
sog in Europe. The American species are larger, the Ptilodus 
4 Pies equaling probably the Norway rat (F ig. 8), while the 
: tus ig ‘sartianus is one-third smaller. The Meniscoéssus conquis- 
a Still larger, equaling about the Polymastodon foliatus (Fig. 
ye Tangement of the crests of the fourth premolar in the 
‘ of Plagiaulacidze differs as follows: In Plagiaulax, Plio- 
ag pi iaulax this tooth is grooved. In Ptilodus the 
tibs ‘ig become so wide (Fig. 8) that the wide intervening 
a. oo narrow keels. In Meniscoéssus there are no 
s the margin of the crown is serrate (Fig. 7 4 £). 
Be E E ES EEEN, 
