KEY TO LAND MAMMALS OF NORTHEASTERN NORTH AMERICA 63 



Species and subspecies 



In this paper subspecies are treated as the component parts of species, 

 not, as is now too often the custom, as independent forms intergrading 

 with species. The relationship of species and subspecies is thus main- 

 tained exactly parallel with that between genus and subgenus or family 

 and subfamily. ^ The separate keys to the subspecies under each species 

 will help to emphasize this conception. I have attempted to apply a 

 system of English names that will coincide with this treatment of species 

 and subspecies, but in certain cases perfect adherence to this principle 

 has not been possible. 



General plan of the key 



Beginning with the definition of the class Mammalia, this paper 

 consists of a series of keys and definitions, interspersed with brief state- 

 ments of range, habitat and extent of groups. Keys are given under 

 each order to its families, under each family to its genera, under each 

 genus to its species and under each species to its subspecies. Suborders, 

 subfamilies and subgenera are not included in this scheme, but their 

 characters are referred to in the sections of the keys or elsewhere, and 

 their names are inserted in the synopsis placed before the " key " proper 

 (p. 65-76). Under each species and subspecies will be found references 

 to, i) the first publication of the specific or subspecific name, 2) first use 

 of the bfnomial or trinomial combination, and 3) a recent monographic 

 paper in which the form is described in detail. Absence of the second 

 reference shows that the binomial or trinomial was used by the original 

 describer of the form, or that it is now for the first time published. 

 Absence of the third reference, in cases where the second and third are 



I An example may make the matter more clear. Squirrels of the genus S ci u r u s occur 

 throughout the greater part of the wooded portion of the northern hemisphere. The species vary 

 much in form, and the variations tend to group themselves in such a way that the different groups 

 are recognizable as subgenera, all, however, falling within the definition of the genus S c i u r u s . 

 To the one of these groups of species containing the type species of the genus the name S c i u r u s 

 in a subgeneric sense is restricted. It happens that this subgenus Sciurus is conflned to (he 

 old world, and that within our limits the genus is represented by the three subgenera T a m 1 a - 

 sciurus, Neosciurus and Parasciurus. No one would on this account deny that the 

 genus Sciurus occurs in eastern North America. A species of this genus, Sciurus ludovici- 

 anus, is widely distributed in the southern United States. Individuals of this species vary con- 

 siderably in size and color, and the variations so group themselves that several subspecies are 

 recognizable, each restricted to a particular part of the range of the species, and all included within 

 the definition of the species. The one of these which was first named (that of the Mississippi 

 valley) and which consequently gives its name to the species as a whole, is not found east of the 

 Aileghanies, where It is replaced by S. ludovicianus vlcinus. Thespecies Sciurus ludo- 

 viclanus is nevertheless as truly a member of the fauna of the eastern United States as is the 

 genus Sciurus. 



