OF THE AUSTKALIAN MAESUPIALIA. 157 



Sectorial Fremolm^s. — The posterior upper teeth may be taken as typical of these 

 elemenls, which include the upper and lower mpdian and lower posterior teeth. Their 

 modifications are of interest as throwing a side-light on the evolution of the series, since 

 they are not connected with the development of the grazing habit, but wdth the passage 

 of the shoot- or twig-eating habit. In their general character they preserve the orthal 

 position in the jaw, as in the Potoroinse. They are never so well developed as in tlie 

 typical shoot-eating forms of the biachyodunt series. In Onychogale the teeth are 

 extremely small as compared with the first molars. They are pear-shaped in section, the 

 larger end being posterior. There are tliree cusps — two outer, and one inner and 

 posterior: the former apj^ear to represent tlie fore and aft portions of the cutting-edge 

 of Caloprymnrts, and the latter the postero-internal cusp. In Lagostrophus, Lagorchestes, 

 and Pefrogale the posterior premolars are fairly well developed. In the first-named 

 genus and in Lagorchestes hlrsutus the teeth are equal in length to the first molars, and 

 their cutting-edges bear three well-developed grooves ; in Lagorchestes conspicillatus, 

 L. lepioroides, and Petrogale they are slightly longer than the first molars and bear four 

 grooves on their cutting-edges. Among the Small Wallabies, M. IFUcoxi, M. Thetldis, 

 31. stigmaticus, and 31. Blllanlieri have the posterior i^remolars equalling in length the 

 first molars, with the tip of the anterior crest of the second, Avith tAvo grooves on 

 the cutting-edges. In 31. Evgenii and 31. Bedfordi the length of the posterior jii-emolars 

 is almost equal to that of the first molars ; the postero-external cusp tends to be 

 grooved. The whole condition is not far removed from that seen in Onychogale. 

 Among the Large Wallabies we find 31. riiJicoUis, 31. Parryi, and 31. Greyi showing a 

 similar approximation to Onychogale ; the posterior premolars are here shorter than the 

 first molar>-. In 31. agilis, on the other hand, the teeth are well developed, their length 

 being equal to that of the first molars and the anterior crests of the second. In 

 the Kangaroos the posterior premolars are shorter than the first molars, and resemble 

 those of the small premolared lower forms. The explanation of these facts seems to be 

 that in the lower genera, including the Small Wallabies, there has been local elaboration 

 of sectorials in connection with a shoot-eating habit, gi'azing adaptations being incomplete 

 at that stage. Small-premolared and large-i^remolared Small Wallabies have apparently 

 given rise to similarly conditioned Lai-ge Wallabies. Tlie relatively small size of the 

 posterior premolars in the Kangaroos ajipears at first sight to indicate that elaborated 

 sectorials have formerl}'- been present in some of the low^er forms and have been sub- 

 sequently reduced ; but the more probable explanation is that these animals are th(> 

 descendants of successively small-pi-cmolared Small and Large Wallabies, wiiich hav(! 

 become more and more dependent on grazing habit and the development of grazing 

 adaptations. 



Canines. — With the partial exception of Lagorchestes con.'ipricillalKs, none of the 

 members of this group show such well-developed canines as those of the brachycdont series 

 (excepting Setony.x), the Potoroinjc and Bettongiina?, although even in the latter they 

 are greatly reduced. These teeth are present in a vestigial condition in Lugorchesles 

 hlrsutus and L. leporoides, vestigial or absent in Onychogale, and typically absent in the 

 remaining forms (except X. conspicillatus). 



22* 



