DIDELPHVIDA 133 
8. Teeth rooted. Three upper incisors and acanine. Hind 
limbs not disproportionately large. Feet syndactylous, 
broad, with four subequal outer toes, and a large 
opposable hallux. Phalangeride. 
y. Teeth rooted. Three upper incisors, and frequently a 
canine. Hind limbs disproportionately large, with 
syndactylous feet as in Peramelide. Macropodide. 
Suborder POLYPROTODONTIA. 
The leading characters of this group are given in the foregoing 
schedule. This group is the only one represented at the present 
day, and so far as we know also in past epochs, beyond the confines 
of the Australasian region and adjacent islands. 
Family DIDELPHYID. 
Dentition: i $,¢ 4, p 3, m 4; total 50. Incisors very small 
and pointed. Canines large. Premolars with compressed pointed 
crowns. Molars with numerous sharp cusps. The last premolar 
preceded by a deciduous multicuspidate milk-molar, which remains in 
place until the animal is nearly adult (Fig. 34). Limbs of moderate 
development, each with five complete and distinct toes, all of which 
are provided with short, compressed, 
curved, sharp claws of nearly equal 
size, except the first toe of the hind 
foot or hallux (Fig. 37), which is large, 
widely separable from the others, to 
which it is opposed in climbing, and 
terminates in a dilated rounded ex- 
tremity, without a nail. Tail gener- 
ally long, partially naked and prehen- 
sile. Stomach simple. Czcum of 
“small or moderate size. Pouch gener- 
ally absent, sometimes represented by 
two lateral folds of the abdominal 
integument, partially covering the 
teats, rarely complete. Vertebre : 
C7, D 13,L 6,8 2, C 19-35. 
The Didelphyide, or true Opos- 
sums, differ from all other existing Fic. 37.Skeleton of the right hind 
Marsupials in their habitat, being feotof the Virginian Opossum (Didelphys 
: : . marsupialis). 
peculiar to the American continent. 
They are mostly carnivorous or insectivorous in their diet, and 
arboreal in habits. 
Opossums occur throughout the greater part of the American 
