162 
The cerebrum does not overlap the cerebellum; the olfactory lobes are 
large. 
The characters given above are diagnostic of a remarkable order of 
mammals, confined at present to the Australian and Austro-American 
provinces. About twenty species are recognized in South America; 
one widely-distributed species is found in North America. 
The order Marsupialia contains a great variety of forms, representing 
most orders of mammals—the Primates by the Phalangers, the Carnivora 
by the Dasyurians, the Ruminants by the Kangaroos, and the Edentates 
by the Monotremes. 
No Marsupial Bats are known, and the Rodents are represented among 
Marsupials by a single species. 
Aside from the pouch and marsupial benes, the most notable feature of 
the order is the premature birth of the young, as compared with other 
mammals. The young of the Great Kangaroo (Macropus major), observed 
by Owen, in 1833, did not exceed an inch and a quarter, from nose to 
end of tail, twelve hours after birth, and the skin had the color and 
semi-transparency of the Karth-worm. 
The dentition is unlike that of any placental mammals; in these the 
normal number of incisors is six in each jaw, but in the marsupials they 
vary from ten above and eight below, to eight above and six below, or 
even six above and two below. Ordinarily there are four true molars. 
Several families of marsupials are recognized. The Didelphidx are pe- 
culiarly American, and the only family to be here considered. 
FAMILY DIDELPHIDA. 
Family Characters—Incisor teeth 272; canines 4:+; premolars 3:3; mo- 
lars $3. The great number of incisors—ten above and eight below— 
readily separate the Didelphidx from all other families of mammals. The 
prehensile tail is usually very long, nearly naked, and covered with a 
scaly skin, from which grow a few scattered hairs. The feet are five-toed, . 
and plantigrade. 
The Opossums are small; the largest is but little larger than a large 
Cat, while the smallest is but little larger than a small Mouse. 
GrENvs DipE.pHys Linneus. 
Didelphys, Linneeus, Systema Nature, i, 1735. 
Generic Characters.—The generic characters of Didelphys are essentially 
those given under the family heading. . 
The genus is restricted to the species having the toes free, and the fur 
of the back thickly interspersed with long, coarse hair. Of this partic 
