Fes., 1912. MamMats or ILLINOIS AND WIscoNnsIN — Cory. 51 
SUBORDER POLYPROTODONTIA. 
Family DIDELPHIID4Z. Opossums. 
The members of this family are confined to North, Central and 
South America. They are pentadactylous and the tail is usually long 
and prehensile. The majority are arboreal and mainly insectivorous, 
but many of the larger species eat birds, eggs, reptiles, etc., and one 
tropical species is semiaquatic and is said to subsist largely upon fish. 
Our species of Opossum seems to be practically omnivorous. 
The teeth are 5oin number. The single species which occurs within 
our limits has a well developed abdominal pouch, but, as has been pre- 
viously stated, in some members of the family it is more or less rudi- 
mentary, being merely composed of two lateral folds of skin separated at 
each end, while in others it is entirely absent. 
Genus DIDELPHIS Linn. 
Didelphis Linneeus, Syst. Nat., X ed., I, 1758, p. 54. Type (by elimina- 
tion) Didelphis marsupialis Linn. 
External abdominal pouch, into which the teats open, well devel- 
oped; feet with five toes; the hind feet with inner toe thumb-like, 
without nail and opposable to the others; ears and tail largely naked, 
the latter prehensile; skull with sagittal and occipital crests strongly 
developed; incisors small and pointed; premolars with compressed, 
pointed crowns; canines large; gape of mouth very large; bristles on 
nostrils and lips, long. 
Dental formula: 1 eS 
4-4 
Didelphis virginiana KERR. 
VIRGINIA Opossum. 
Didelphis marsupialis Linn., Syst. Nat., X ed., I, 1758, p. 54 (in part only). 
Didelphis virginiana Kerr, Anim. Kingd., 1792, p. 173. Haymonp, Rept. Geol. 
Surv. Ind., 1869, p. 205 (Indiana). GARMAN, Bull. Essex Inst., XXVI, 1894, 
p. 7 (Kentucky). ALLEN, Bull. Amer. Mus. Nat. Hist., XIV, 1901, p. 162 
(Illinois, Tennessee, Missouri, etc.). JacKsoN, Proc. Biol. Soc. Wash., XX, 
1907, p. 71 (Missouri). d., Bull. Wis. Nat. Hist. Soc., VI, 1908, p. 14 (Wis- 
consin). McATEE, Proc. Biol. Soc. Wash., XX, 1907, p. 2 (Indiana). Haun, 
Proc. U. S. Nat. Mus., XXXII, 1907, p. 456 (N. W. Indiana). Jb., Proc. U. 
S. Nat. Mus., XXXV, 1908, p. 568 (S. Indiana). Jb., Ann. Rep. Dept. 
Geol. & Nat. Resources Ind., 1908 (1909), p. 448 (Indiana). EVERMANN 
& Ciark, Proc. Wash. Acad. Sci., XIII, 1911, p. 2 (Indiana). 
