380 



CLASSIFICATION OF VERTEBRATES. 



m ^, include the genera Perameles, in which the feet are much alike, and 

 >Chczropus, 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.), 

 Dicrocyttodon (Jurassic, Wyoming), Amphitherim 

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

 etc. 



FIG. 358. Opossum, 

 JDidelphys virginiana, 

 after Audubon and 

 -Bachm'an. 



SUB-ORDER 2. DIPROTODONTA. 



Incisors -, the central ones large, the others 



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-, -h _ _, m !; tail 



i o o y 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 PHALAXGISTID.E includes climbing and flying 



(soaring) forms, with legs of equal size, teeth i . , c -,p ~ , m -, tail long. 



I O 21 4 



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

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

 ilying 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 f , in ^. The kan- 

 garoo-rats, or HYPSIPRYMNID/E, with teeth z |^, c ^, p \ in |, resemble the 

 kangaroos in the disproportionate hind legs. Hypsiprymnus, Bettoiigia, 

 the last also in the Australian pleistocene. The DIPROTODONTID^E in- 

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

 the teeth /' \, c g, p \, m \. Diprotodon attstralis was larger than a rhi- 

 noceros ; the species of Notothenum 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 

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

 Ccenolestes obscunis, has been described from Colombia. 



