476 MR. OLDFIELD THOMAS ON [May 1, 



Percmieles into four, coi-responding to the gi^oups A, c, e', and /' of 

 the cranial synopsis of the species in the ' Catalogue of Marsupials.' 

 These are all natural groups of species, easily distinguishable both 

 by external and by well-marked cranial characters, as follows : — 



IsooDON Desm. 

 Type, /. ohesulus. Other species, macrur%(,s, moreshyensis, 

 auratus, harrowensis. 



Incisors |. Bullte large, complete, pear-shaped. 



ECHTMTPERA LoSS. 



Type, E. doreyana. Other species, cockerelli. 



Incisors |-. Bullfe small, hemispherical, more or less incomplete. 



Perortctes, g. n. 



Type, F. raffrayamis. Other species, hroaclhenti, longiccaulatus, 

 ornatus. 



Incisors -f. BuUee as in Echymipera. Brain-case normal. 

 Lacrymal bone rounded externally. 



Perameles Geoff. 



Type, P. nasuta. Other species, gicnni, hougainvillei, eremiana. 



Incisors |-. Bullee small, hemispherical, complete. Bi"ain-case 

 abnormally short. Lacrymal forming a sharp overhanging edge 

 externally. 



All the Australian species thus fall into Isoodon and Perameles, 

 which were long ago recognised as very different grou^DS by Gould. 

 The other two genera are Papuan. 



With regard to the name used for the first genus, Isoodon, I 

 find on reconsideration that my selection of obesula as the type of 

 Thylacis lUiger was incorrect, as it is in opposition to the sound 

 principle supported by Dr. Allen*, that if a genus contains 

 exactly the same species as an earlier one it is a synonym of that 

 one, and no elimination or selection of difi'erent types can make 

 it valid. For Thylacis (and Thylax Oken also) consisted of obesida 

 and nasuta, which were likewise the constituent naembers of the 

 original Perameles, so that neither Thylacis nor Thylax can be 

 withdrawn from their positions as full synonyms of that genus, 

 and the next name in date, Isoodon, has to be taken for the 

 common Australian Bandicoot. 



28. Dasyurus geoffroyi fortis, subsp. n. 



S . 1,2. Arthur Eiver, Wagin. Alt. 840'. 



Similar in essential characters to true geoffroyi, but larger, the 

 difference specially marked in male skulls. Externally fortis 

 has the belly hairs whiter terminally, while in true geoffroyi 

 they are more or less tinged with creamy yellow. The underside 

 of the tail is dark for a rather greater extent. Skin of palms, 



* Bull. Am. Mus. N. H. xvi. p. 116 (1902). See also Thos., P. Biol, Soc. Wash. 

 XV. p. 153 (1902). 



