OF THE AUSTRALIAN MAESUPIALIA. 91 



The various genera may be arranged on a hasis of their molar and premolar characters 

 as follows : — 



A. Pi'otocoiie of upper molars well developed ; external styles obsolete. Lower 



molars with broad shelt'-like taloiiid ; no metaconid. Posterior premolars 



well developed Thylacininae. 



(jenus : Thijlaciiius. 



B. Protocoiie of upper molars variable ; external styles well developed. Lower 



molars with basin-shaped talonid, whicli is well developed or reduced ; 

 metaconid present, variable. Posterior premolars variable or absent. 



a. Dentition normal ; molar formula Dasyurinae. 



Genera : Sminthopsis, Antechinomys, Phascoi/a/e, C/uetocercus, 

 Dasyuroides, Dasyurus, Surcopkilus. 



b. Dentition retrogressive ; molar formula .^ Myrmecobiinse. 



Genus ; Myrmecobius. 



Dasttjeix-E. 



From the standpoint of their dental sequence, the Dasyurinae may be regarded as 

 forming a continuous progressive series. Every gradation is presented between a 

 primitive insectivorous condition and one indicative of high carnivorous si^ecialization ; 

 there are no divergent developments of any significance, and the ti'ansforraation takes place 

 without reference to generic distinction. The evolution appears to be clpsely connected 

 with increase in si/e of the body, and carnivorous characters are for the most part 

 preceded by carnivorous habit *. 



The general relations of the various forms appear to be as follows : — The two genera 

 Sminthopsis and Anlechlnoviys in general represent the smallest and most primitive 

 members of the series. Although diilV'ring in no essential characters of the dentition from 

 the smaller species o^ Pliascoyalc, they lack the range of modification which is characteristic 

 of the latter genus, and which prevents it from being prototypal to the same extent. 

 The larger species of Pliascogale present specialized characters, such as the reduction of 

 the posterior premolars, Avhich make them transitional between the smaller species 

 of the same genus and those of Dasyio-its, to which they bear an ancestral relation. 

 Of the species of Di(i<yiirus, the form which approximates most closely to Fliaficocjale is 

 D. ludlucafKs, this animal almost repeating the dental characters of 1\ Tf'dllacel or 

 P. TJiorbec'7ci(ii/a. Of the remaining species, J), vkerrinns and D. Geoffro'jl are inter- 

 mediate, both in size and dental characters, between D. hallucatm and J), maculatm. 

 The dental characters of the last-named form are exactly prophetic of those of Sarcophilus 

 iirsinns. The two genera Cheelocet'C/is and Dasynrokles are simply terrestrial modifications 

 of Phoscocjale, and approximate closely in their dental charactci-s to the larger species of 

 that genus and to Dasyiit-iis hallucutus. 



* The familiar aocoimts given by Gonid (1863) and Lydekker (1894) of the habits of these and other Australian 

 Marsupials have been extensively supplemented by Semon (1896). 



SECOND SERIES. — ZOOLGGV, VOL. IX. 11 



