FOSSIL VERTEBRATES — MAMMALIA 825 
Amphitherium, from the Oolite of England, near Oxford. 
Amblotherium, from the Purbeck of England. 
Dryolestes, from the Upper Jurassic of Wyoming. 
The Myrmecobide, Peramelide, Dasyuridea, and Didelphyide are 
all families containing living forms, the last two have members 
from rocks as old as the earliest Eocene. It is of interest to 
note that while the family Dedelphyide, the opossum, is at pres- 
ent confined to the North and South American continents it 
formerly ranged over the whole of Europe and England. 
Diprotodonta.— This suborder is distinguished by the presence 
of only two incisor teeth in the upper jaw and one in the lower. 
The premolars are like the molars, or may be developed as long 
cutting organs, as in the Ad/otherra. There are several families, 
but only two are of interest to us here, as they are the only ones 
that contain fossil forms. The suborder, living forms as well as 
extinct, is entirely confined to the Australian region. 
Thylacoleo is the single representative of the 7hylacoleonidae ; 
it was a large form about the size of the lion, with strong inci- 
sors and one of the premolars in each jaw greatly elongated in 
the antero-posterior direction, and compressed from side to side 
so as to form a long cutting edge; the rest of the dentition is 
quite weak. The posterior part of the head is very wide, but it 
narrowed rapidly as itapproaches the anterior end. 
LDiprotodon and WNototherium are the representatives of the 
Diprotodontidae. The skull of the first was nearly three feet 
long, the incisor teeth were developed as gnawing teeth, with 
enamel on the outer side only and set in deep alveoli. The pos 
terior teeth lacked the cutting edges of Thylacoleo, and were 
adapted to grinding up vegetable material. The whole form had 
the bulk of the rhinoceros; the structure of the feet is unknown. 
Nototherium was very similar to this form, but was considerably 
smaller. 
EuTHERIA: Animals in which there is no marsupium; the 
embryo is nourished by the development of a placenta that 
attaches it to the mother. This includes all the remaining forms 
of the mammals. Palaontologists recognize ten orders of the 
