AMERICAN OPOSSUMS 



155 



course the chief interest of the genus, which may he " an un- 

 inoditied survivor from Mesozoic times, and therefore from a 

 time long hefore the Didelphyidae, Peramelidae, and Dasyuridae 

 were differentiated one from the other." Another ancient feature 



Fig. 82. — Bandeil Aiistraliau Aiiteater. M i/rmfailiii(s fasciatus. 



(found in Jurassic mammals) is a mylo-hyoid groove upon the 

 lower jaw, which, however, is not always present, and its exist- 

 ence has therefore heen denied. The single species, M. fasciatus, 

 is partly arboreal and partly terrestrial in habit, and feeds upon 

 ants. It is a Western and Southern Australian form. 



Fam. 2. Didelphyidae. — All the members of this family are 

 pentadactylous. The 

 teeth are fifty in number, 

 arranged thus : 1 1^ C -^ 

 Pm jl M 1^. The caecum 

 is small ; the pouch is 

 generally absent ; the 

 tail generally long and 

 prehensile. 



The genus Dideljjhys 

 contains most of the 

 forms belonging to this 

 family, including as it 

 does some twenty -three 

 species. The Opossums 

 are mainly arboreal ani- 

 mals, insectivorous in Fi«- 83. — Virginian Opossum. Didelphysrirginiana. 

 ,1 . ^ , 1 . .. 1 X i. (After Vogt and Speclit.) 



their lood ; but the larger 



species eat reptiles, birds, and their eggs. Several of the small 



species carry their young, when aljle to leave the teats, on 



