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 bones, 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 Earth-worm. 



The dentition is unlike that of any placental mammals ; in these the 

 normal number o'f incisors is six in each jaw, but ia 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 DIDELPHIDiE. 



Family Characters. — Incisor teeth fil; canines \z\; premolars |:f; mo- 

 lars ^'.^. 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. 



Genus Didelphys Linnteus. 



'Hdelphys, Linnasus, Systema Naturse, i, 1735. 



'''eneric Characters. — The generic characters of Didelphys are essentially 

 ' given under the family heading, 

 genus is restricted to the species having the toes free, and the fur 

 ack thickly interspersed with long, coarse hair. Of this partic 



