MAMMALIA 357 



SUB-ORDER 2. DIPROTODONTIA 



The members of this division are mainly herbivorous. Their 

 dentition is not unlike that of the rodents, the incisors being of the 

 gnawing type, usually two pairs above and one pair below. The 

 canines are either small or absent; the molars have either tubercles 

 or transverse ridges. This group contains the largest and most highly 

 specialized of the marsupials. 



Family 7. Epanorthidce. This family consists of various extinct 

 forms and the single living genus Ccenolestes (marsupial shrews), the 

 only American diprotodonts. It is native to Andean foot-hills of 

 South America. The affinities of this genus are still somewhat in 

 doubt, but Osgood, in an unpublished monograph on the genus, claims 

 that it is in a sense intermediate between the polyprotodonts and the 

 diprotodonts. It has a primitive diprotodont dentition, but a foot 

 structure more like that of the polyprotodonts. Its resemblances to 

 Perameles are rather striking, but these may be homoplastic in 

 character. Osgood considers that the ancestor of Ccenolestes was a 

 North American form, which also may have given rise to the early 

 diprotodont stock that migrated to Australasian territory. In gen- 

 eral appearance Ccenolestes is one of the most generalized of mar- 

 supials, reminding one more of the shrews than anything else. Many 

 of its anatomical features are also very generalized, a fact that is in 

 harmony with its close resemblance to a long extinct group, that 

 lived in Miocene times. The name Ccenolestes means "a modern 

 representative of an ancient group." 



Family 8. Phalangeridce (Phalangers). This is one of the largest 

 marsupial families and consists mostly of arboreal forms. They are 

 characterized by having five fingers and toes, with the second and 

 third phalanges bound together by an integumentary bond ; the hallux 

 is usually opposable. The pouch is well developed ; the tail is usually 

 long. The following are some of the more important genera: Tarsipes, 

 the long-snouted phalanger; Acrobates, the pigmy flying phalanger; 

 Distoechurus, the pen-tailed phalanger; Dromicia, the dormouse 

 phalanger; Petaurus, the true flying phalangers; Tricosurus, the true 

 phalangers; Phascolarctus, the koala or marsupial bear. 



The true phalangers (Fig. 185, F) are fairly large forms, more or 

 less fox-like in form and sometimes known as " brush-tailed opos- 

 sums." The flying phalangers are much like our flying squirrels in 



