6 EXTINCT GENUS OF MARSUPIALS ALLIED TO HYPSIPRYMNODON, 



a ridge which forms the posterior half of the diastema (Il^psi- 

 prymnodon, Phalangista) ; this ridge is defined on the outer side 

 by a compression of the incisive socket beneath {Hypsiprymnodon, 

 Phalangista), on the inner by a superficial groove between it and 

 the articulating surface of the symphysis. Midway between the 

 end of the canine socket and the premolar a depression marks the 

 site of an anterior premolar {Phalangista, Hypsiprymnodon). The 

 anterior orifice of the dental canal is large {Phalangista) and 

 much in advance of the premolar {Hypsipi'ymnodon). The con- 

 vexity of the lower edge of the jaw is greatest beneath the molars 

 {Hypsiprymnus). The hinder part of the ramus is broken away, 

 but a small portion of the anterobasal edge of the ectocrotaphyte 

 fossa is preserved sufficient to shew by its inner surface directed 

 forwards and downwards that it was widely perforated in con- 

 tinuity with the dental canal [Hypsiprymnodon, Hypsiprymnua). 



Teeth. — The incisor is strong and relatively short {Hypsiprym- 

 7ius), quadrilateral, cuneiform, its sides deep at the base and 

 tapering rapidly forwards. Its upper surface is a continuous 

 plane of wear, slightly concave longitudinally, and narrowing as it 

 nears the base ; its lower surface, moderately convex both trans- 

 versely and longitudinally, is well clothed with enamel, which 

 extends over the lower third of the lateral surfaces, and conse- 

 quently surrounds and arms with a cutting edge the apical third 

 of the tooth only ; its lateral surfaces are flat, parallel, equal, and 

 similar. On the upper end of the enamel of the inner lateral 

 surface a distinct but small area, flattened and polished by wear, 

 extends as a triangular facet a short distance downwards, indi- 

 cating a laxity of the symphysial ligament not sutticient to allow 

 of attrition between the incisors to so great an extent as in the 

 Kangaroo Rats. The canine is absent ; its large open socket shews 

 it to have been a functional tooth, though liable to be shed (Hypsi- 

 prymnodon, Phalangista). The premolar, in form a short oval, 

 as broad as high at its posterior end [Pludangista, Hypsiprymno- 

 don) is rather longer than it is high ( Hypsiprymnus approxima- 

 tively) it is placed obliquely in the jaw, its degree of obliquity 



