2 BULLETIN 128, UNITED STATES NATIONAL MUSEUM. 



a name was based. The sequence of groups is in its main features 

 that adopted by Osborn in his "Age of Mammals," 1910, and by 

 Cabrera in his "Manual de Mastozoologia," 1922. In the arrange- 

 ment of families and genera an attempt has been made to bring the 

 sequence as far as possible into harmony with that of the higher 

 groups — to begin with the more primitive forms and to end with 

 those which present the highest total of specialization,^ Under every 

 species and subspecies reference is made to the first publication of 

 the specific or subspecific name. To this, when necessary, is added 

 (a) reference to first use of the current binomial or trinomial; (b) in 

 the case of species described before 1885, but not at that date admitted 

 as valid, reference to their establishment as members of the North 

 American fauna; (c) reference to True's list; ^ and (d) references to 

 changes of such names as are now different from those used by True. 

 References to alterations in generic names are also given, but the 

 concordance with the nomenclature of 1885, being indicated by the 

 citations under species, is here omitted. The type locality of each 

 form is stated with all possible exactitude, and in revised genera the 

 ranges are given, so far as practicable, in the words of the author of 

 the revision. Authors' names are placed in parenthesis when two 

 references are required to explain the combination here adopted. 

 All questions of nomenclature have been decided as nearly as possible 

 in accordance with the International Zoological Code. 



Class MAMMALIA. 

 Subclass EUTHERIA. 



Superorder DIDELPHIA. 



Order MARSUPIALIA. 



Suborder Polyprotodontia. 



Family DIDELPHIID^. 



Genus DIDELPHIS Linnaeus.^ (Opossums.) 



1758. DidelpMs Linn^us, Syst. Nat., ed. 10, vol. 1, p. 54. Type, 

 DidelpMs marsupialis Linn^us. 



<• The term total of specialization is here used to denote the sum of the physical modifications which any 

 particular mammal or group of mammals is supposed to have undergone during the course of its develop- 

 ment away from an assumed original or generalized mammaUan stock. In this computation no idea of 

 "excellence," "efiaciency," or their contraries is involved. This portion of the work, together with a 

 review of the status of genera and subgenera, is the result of original investigation. Elsewhere the strictly 

 historical method has been adhered to as closely as possible except in cases where it would cause the 

 perpetuation of confusing errors. 



• No attempt is made with the many species which prove to have been composite as understood in 1885 

 to apportion the name then used to each of the component parts as they now stand. 



I Revised by Allen, Bull. Amer. Mus. Nat. Hist., vol. 14, pp. 149-188, June 15, 1901. 



