OF THE AUSTKALIAN MAESUPIALIA. loo 



that, ns in more primitive forms, all of the teeth are functional at the same time. In 

 the present series the first molars may be worn to the bases of their transverse ridges 

 before (he fourth teeth come into place. This functional rotation is much more 

 conspicuous in the Kangaroos than in other forms, and has there been aptly compared 

 by Tliomas (1888) to that found in the Proboscidea and some Sirenia. Correlated -with 

 the functional rotation is a throwing-oflf of the worn-out anterior teeth. On examining 

 a series of individuals of different ages, it is seen that the worn median premolars and 

 milk -premolars are first thrown off by the eruption of the posterior premolars, and that 

 afterwards the latter, and finally the first molars, are thrown off; so that, of seven 

 cheek-teeth, only the last three to appear remain. In the Kangaroos that portion of the 

 margin of the jaw which bears the cheek-teeth is raised above the anterior edentulous 

 portion ; and De Vis, in his interesting paper on the fossil Kangaroos, has pointed out 

 that the anterior teeth are in a way pushed over the edge of this platform, the posterior 

 premolars not being large enough in these forms to retain their own position and that of 

 the succeeding first molars. However this may be, the condition in the Kangaroos 

 represents a distinct adaptive advance on that in the Wallabies, where even in small 

 premolared forms the anterior teeth are retained. 



Hypsodontism of the molar crowns is more pronounced in the Kangaroos (PI. 5. fig. 23 

 & PI. 6. fig. 29, Macropiis rtifns) than in the smaller forms (PL 5. fig. 21 & PI. 6. fig. 27, 

 Lagorchestes), and is better indicated in all of the group than in Bendrolagus or Dorcojjsls. 

 31. Eugenii furnishes a partial excej)tion, the length of the molar crests in this form beini^' 

 scarcely greater than in the last-named genera. 



In respect to the molar patterns, the present group shows an advance on the brachyorlont 

 series in the formation of longitudinal crests supplementing the transverse ones. Mention 

 has already been made of the presence in the Phalangerinse, the Bettongiinue, and 

 Potoroinse of longitudinal bands connecting the protocone and hypocone in the upper 

 molars and the protoconid and hypoconid in the lower, and ending anteriorly and 

 posteriorly in both cases in thin ledges. In the brachyodont series these elements are 

 scarcely indicated; but in the present group they appear as longitudinal crests. One of 

 these crests connects the anterior and posterior transverse crests. It is placed on the 

 internal side in the upper mclars and on tlie external side in the lower. The up])er 

 longitudinal element opposes the posterior transverse crest of a lower tooth, wiiile the 

 lower longitudinal crest opposes the anterior transverse crest of an upper tooth. In tiic 

 lower teeth the longitvulinal band is represented in front by a ridge extending from 

 the tip of the protoconid to the anterior ledge. Passing from such a type as ihdo- 

 frymnus (PL 6. fig. 25) to the Kangaroos (PL 6. fig. 28), we find this ridge assuming a 

 more internal position, its outer wall becoming pouched in such a way that a structure 

 resembling the antero-external shelf of polyprotodonts is formed. In the upper molars 

 the anterior ledge has lost its connection with the protocone, but tends to be connected 

 externally with the paracone. This connection is obvious in all of the forms, uilh the 

 exception of the Large AVallabies and Kanj^aroos : in the former it is barely indicated, 

 while in the latter the anterior ledge is practically free externally. In the Kangaroos 

 an apparently new ridge is developed internally. It is well developed in all forms 



SECOND SERIES. — ZOOLOGY, VOL. IX. 22 



