458 dr. e. a. goeldi as the [June 5, 



the subgenus Didelphyt — D. marwpiati* — with two varieties: 

 1). ma ■i-s" infills fi/jiirft, very widely spread over the American 

 continent and including even D. virgimana and J), californica of 

 other zoologists, with a range extending to Chili and Brazil ; 

 I), uifirsiipialis var. azrira>, on the other hand, being confined to 

 the countries bordering the Amazonian Basin, but ranging on the 

 eastern coast to South Brazil. The characters are purely external 

 and may be briefly referred to as follows: — Face without, or with 

 indistinctly defined, black and white markings — var. typica\ face 

 with sharply defined black and white markings— var. azorcB. In 

 the list given of the specimens contained at that date in the 

 collection of the British Museum from Brazilian localities 1 find 

 four of var. typica (3 from "Brazil," 1 from "Bio de Janeiro'') 

 and two of var. azara ( both from Taquara, Bio Grande do Sul, 

 collected by my friend and colleague Dr. H. von Ihering). 



Well, according to the exposition of Mr. Oldfield Thomas, there is 

 absolutely no doubt that I should have to determine my specimens 

 from the Serra dos Orgaos as belonging to 1). martitpialis var. 

 t>/pica. 



To anybody who has occupied himself seriously with the study of 

 Marsupials, it is evident that the family Didelphyidae in general, 

 and the genus DideHphys in particular, is, even in our days, \\ hat is 

 called a " crux zoologica." On this point Mr. Oldfield Thomas 

 says : — " With the exception of the short-tailed Opossums the series 

 available for examination in the European museums seems to be 

 fairly complete, but in the case of these more specimens are 

 urgently needed before the species can be at all satisfactorily 

 worked out and the present arrangement of that, the most 

 difficult, group must be looked upon as merely tentative in its 

 nature." And some lines above he writes: — "The systematic 

 arrangement of the Opossums has formed the subject of an 

 unusually large number of memoirs, of which the best have been 

 written by Temminck, Waterhouse, and Burmeister. These and 

 all other authors appear, however, to have erred in the admission 

 of by far too great a number of species, formed on the most trivial 

 characters of colour and size, and therefore a large reduction has 

 been found to be necessary in the present work." 



I perfectly agree with Mr. Thomas as to the great difficulty 

 presented by the group, and I even partly share his opinion that 

 the number of species admitted by former authors is too large 

 and that the synonymy has been much overburdened. But when 

 he chooses the radical method of cutting the Gordian knot by con- 

 densing all the species into one and grouping all older synonyms 

 around two varieties only, it seems to me that he goes too far. 



On reviewing the writings of the three principal authors who 

 have discussed the Mammals of this region — Burmeister 1 *, 



1 ' Systeinatisclie Uebersicht der Thiere Brasiliens, welclie wiilircnd einor 

 Reise durch die Provinzen von Rio de Janeiro and Minaa ft mn It 

 oder beobachtet wurden,' vol. i. (1854). 



2 ' Erlauteruneen zur Fauna Brasiliens,' Berlin, 185G. 



