OF THE AUSTRALIAN MAESUPIALIA. 151 



other hand, it is much more comprehensive, the herbivorous adaptations being taken iip 

 at a stage not far in advance of that represented by Caloprymmis, and rapidly brought to 

 a higli state of perfection. 



The extent of modification may be briefly summarized as follows:— (f/) In the molars, 

 complete conversion of the anterior and posterior pairs of cusps into transverse crests, 

 the latter becoming successively elongated ; development of longitudinal crests from 

 already existing longitudinal bands, or as new structures; reversal of the relative pro- 

 portions of the teeth, by which they come to inci'ease in size backwards ; retardation of 

 the posterior teeth, with functional replacement from behind forwards. (6) In the upper 

 incisors, reduction of the length of the median upper teeth, by which they cease to project 

 beyond the lateral ones; compression of their edges ; elongation of the cutting-edges of 

 the lateral teeth, frequently accompanied by reduplication, [c) In the lower incisors, 

 perfection of tbe spatulate development, by which they come to cut against all of the 

 upper incisors, and in some cases against one another, [d) In the canines, rapid 

 obliteration proceeding from an already reduced condition, (e) In the median and 

 jiosterior premolars, successive elaboration of the teeth as sectorials. 



As mentioned above, the dental evolution of the existing Macropodinae appears to have 

 proceeded along two different lines. One of them is represented as a series of typical 

 forms, whose evolution has been a terrestrial one throughout and has culminated in the 

 true Kangaroos; while the other is represented by an aberrant series, whose evolution, 

 at least in the ease of two genera, has been effected by a return to arboreal life. In the 

 following descriptions these groups are respectively referred to as the hypsodont and 

 brachyodont series. 



The Brachyodont Series. (Dendrolagus, Dorcopsis, Setonyx.) 



The derivation of Dendrolagus and Dorcopsis is an interesting question, on account of 

 the fact that while both forms are more primitive in their general dental characters and 

 more specialized in their premolar characters than the true Kangaroos, Dorcopsis appears, 

 and has been commonly supposed from its terrestrial habit and its limb proportions, to 

 represent a connecting-link between the latter and the tree-living Dendrolagus. On 

 tracing the dental sequence, it is found that neither one of the two genera is nearly 

 related to the true Kangaroos, the resemblances shown by Dorcopsis to the latter being 

 the result of convergent development. The evolution appears to represent a Papuan 

 migration, the sequence of species being as follows : — Dendrolagus Lumholtzi and 

 D. Bennettianus (Queensland forms) ; D. inustus, D. Dorianus (both Papuan forms) ; 

 Dorcopsis Macleayi, D. luctuosa, D. 3Iuelleri (all Papuan forms). The species of 

 Dorcopsis are derivatives of Dendrolagus Dorianus, or a closely allied form, which have 

 become terrestrial and have begun to assume characters similar to those of the true 

 Kangaroos. 



The relations of Setonyx {— Macropus brachyurus, Quoy & Gaim.) are rather obscure. 

 It resembles Dorcopsis and Dendrolagus in the characters of its incisors and molars, and 

 also in the general characters of its sectorial premolars. In the relative size of its 



