or THE AUSTKALIAN MAllJSl TIALIA. 203 



the more southern 31. Greyi, and a similar relation is observable between M. Bedfordi 

 and 31. dorsalis. The existing Kangaroos are apparently the descendants of successively 

 small-premolared forms. 



TH Y LACOLEONTID.E. 



The evidence available concerning the phylogenetic position of Thijlacoleo is very 

 incomplete, partly on account of the absence of annectant types, and partly because 

 of the lack of information as to the foot-structure. The dentition furnishes indications 

 of two lines of development — one of normal 2)halaugerid type, represented by the 

 diprotodont modification, involving enlargement of the median incisors and reduction of 

 the posterior antemolar teeth, and by the enlargement of the posterior premolars as 

 sectorials ; the other of a special carnivorous type, represented by the inercing develop- 

 ment of the median incisors, the reduction of the molars, and the excessive enlargement 

 and smoothing of the cutting-edges of the sectorials. This evidence does not warrant a 

 closer estimation of the relations of the animal than that it is a derivative of the 

 Phalangeridse, which, unlike all the remaining derivatives of that family, has, after 

 the passage of the omnivorovxs stage, or even dviring the herbivorous stage, become 

 carnivorous instead of continuing tiie herbivorous evolution in the normal way. 



PHASCOLOMYID^ and DIPROTODONTID.E. 



Th<$>vailable evidence concerning the phylogenetic position of these families may be 



briefly dimmed up as follows: — It is possible to recognize, both in the dentition and 



foot-stn?^jj.g^ three kinds of characters — primary ones of phalangerine affinity, secondary 



ones 01 a.^jj^y with one another, and characters of divei-gence. The first refer to the 



diprotodonu^g^^.j^g,.g^. q£ ^|jg dentition and the bunodout origin of the molars, and, in 



the foot-str\y^j.g^ ^ljg reduction of the second and third digits, enlargement of the 



fourth, and 0\)sability of the hallux. The second refer to the rodent modifications of 



the mcisors, t V^i^ction of the premolars to the posterior paii-, which present somewhat 



similar patterns\j ^j^^ terrestrial plantigrade modification of the pes. The divergent 



characters reiei iai ^ retention in the Diprotodontidte of tlic upper lateral incisors, tlie 



presence oi lop 0"\ rooted molars, and the shifting of the walking axis to the outer 



side of the pes, wi .largement of the astragalus, calcaneum, and cuboid, fusion of the 



mesocuneiform ^^^i^^H gntocuneiform, and functional retention of the hallux as an 



internal balancei. Xphascolomyidse the upper lateral incisors have been obliterated, 



and the molais i \ ^ rootless and rodent in their character while remaining 



bunodont. There has \ j-g.^ig^-giop^j^gnt of the second and third digits by which the 



shifting of the walkmg a.V ^^^ ^^^ ^,^^ ^^^^ avoided. The latter is thus of a more 



normal or less ^^^"^y'^'^^^'^^%. The entocuneiform has remained distinct from the 



mesocuneiiorm. ' \not been modified as a balancer, but has been reduced 



in the same way as in other ^^^.^^ ^^^^^^ 



SECOND SERIES.— ZOOLOGY, v^^ ^^ 



