380 



CLASSIFICATION OF VERTEBRA7ES. 



.m , include the genera Peraineles, in which the feet are much alike, and 

 <Ch<zropus, in which the hind legs are very long and the fourth toe alone 

 functional. The bandicoots (Perameles) are no- 

 ticeable from the existence of a placenta. Fossils, 

 which in some respects closely resemble the polypro- 

 todonts and in some the insectivores, are the TRI- 

 CONODONTA and TRITUBERCULATA, with the genera 

 Amphilestes, (Jurassic, England and the U. S.), 

 Dicrocynodon (Jurassic, Wyoming), Amphitherim 

 (English oolite), Dryolestes (Jurassic, Wyoming), 

 etc. 



SUB-ORDER 2. DIPROTODONTA. 



FIG. 358. Opossum, 

 )idelphys virginiana, 

 after Audubon and 

 -Bachman. 



Incisors -, the central ones large, the others 



'73 



reduced ; canines small or absent ; molars with 

 blunt tubercles or transverse ridges. 

 In the kangaroos and wallabies (MACROPODID/E) the hind legs are very 



large: the feet as in Perameles ; the teeth / _, c or- 



i o o 



2 or I 4 .. 



, in - : tail 



2 or I 4 



very large. The larger kangaroos belong to Macropus ; the arboreal tree- 

 ikangaroos to Dendrolagus. Macropus, Palorchestes, etc., occur in Austra- 

 lian pleistocene. The PHALANGISTID^E includes climbing and flying 



((soaring) forms, with legs of equal size, teeth /' . , c -,p -, in -, tail long. 



Tarsipes is an aberrant form about as large as a mouse. Petaurus, Be- 

 lidius, etc., resemble the flying-squirrels in the lateral fold of skin and 

 flying habits. Cuscus and Phalangista resemble the opossums in their 

 prehensile tail. Phascolarctos, the koala, contains but a single climbing 

 species two feet long. The THYLACOLEONID/E includes large fossil forms 

 from the Australian pleistocene, with teeth i ^, c \, p , m \. The kan- 

 garoo-rats, or HYPSIPRYMNID^:, with teeth i\, c \, p \ m |, resemble the 

 Icangaroos in the disproportionate hind legs.. Hypsipryinnns, Bettongia, 

 the last also in the Australian pleistocene. The DIPROTODONTHXE in- 

 cludes only fossil forms of large size from the Australian pleistocene, with 

 the teeth i ^, c , p ^, m |. Diprotodon australis was larger than a rhi- 

 noceros ; the species of Notothertum somewhat smaller. The PHASCOLO 

 MYID^E, with a dental formula i \, c , p \, m |, differ from all other mar- 

 supials in the presence of persistent dental pulps. The living wombats all 

 -belong to Phascolomys, which also occurs in the pleistocene. The extinct 

 Phascalonus was as large as a tapir. South America has yielded several 

 fossil diprotodonts of eocene or miocene age, and one recent species, 

 Ctznolestes obscunis, has been described from Colombia. 



