250 Bulletin American Museum of Natural History. [Vol. XV I, 



in the same manner and to the same degree as the northern 

 members of the group. 



HISTORICAL RESUME AND NOMENCLATURE. 



As in the case of the North American forms, the South 

 American present puzzling questions of synonomy, some of 

 which have already in part been considered. 1 The first name 

 applied as a species name to any member of the restricted 

 genus Didelphis was marsupialis (Linnaeus, Syst. Nat., 1758, 

 p. 54), given to a group of forms comprising all the large 

 opossums then known. Owing to this fact various writers, 

 from Temminck and Waterhouse down to the present time, 

 have treated the name as indeterminate. There is no doubt, 

 however, of its exclusive relation to the large opossums of the 

 restricted Didelphis group; the trouble is satisfactorily to 

 fix the name upon some one of the several components of the 

 original marsupialis. 



At one time I favored restricting the name marsupialis to 

 the Virginia opossum (this Bulletin, XIII, 1900, p. 187), on 

 the ground that the reference to Tyson was the first of the 

 citations given by Linnaeus that was positively identifiable. 



Later (op. cit., XIV, 1901, p. 164), through the application 

 of the principle of elimination, I favored fixing the name on 

 the large Mexican species, on the basis of the Linnaean refer- 

 ence to Hernandez, the large Guiana form having been taken 

 out of the group by Zimmermann in 1780, the Virginian 

 species by Kerr in 1792, the Paraguayan and South Brazilian 

 respectively in i8"i6 and 1826, leaving only calif ornica of 

 Bennett of the members originally composing it. Mr. Old- 

 iield Thomas, however, has objected to this (Amer. Nat. 

 XXXV, Feb. 1901, p. 144; Ann. and Mag. Nat. Hist. (7) 

 VIII, Aug. 1901, p. 153), on the ground that Linnaeus's only 

 reference in the sixth edition of the 'Systema Naturae,' and 

 the first in order of sequence in the tenth edition, is to Seba, 

 and that Seba's animal is beyond doubt the ordinary large 

 dark opossum of northeastern South America, subsequently 

 named Didelphis karkinophaga. Although at one time I was 



1 Cf. this Bulletin, XIII, 1900, pp. 185-187. 



