12 KENDALL: NEW ENGLAND SALMONS. 



readily distinguished from one another. When, on the other hand, we have "represen- 

 tative species", — closely related forms, neither of wlaich is found within the geographi- 

 cal range of the other, — we can with some confidence look for intermediate forms where 

 the territory occupied by the one bounds that inhabited by the other. In very many 

 such cases the intermediate forms have been found; and such forms are considered 

 as sub-species of one species, the one being regarded as the parent stock, the other as an 

 offshoot due to the influences of different environment. Then, besides these "species" 

 and "sub-species", groups more or less readily recognizable, there are varieties and 

 variations of every grade, often too ill-defined to receive any sort of a name, but still 

 not without significance to the student of the origin of species.' 



These quotations are explanatory of the statement that the word 'species' is one of 

 convenience. In other words, it affords the means of labelling specimens in collections, 

 which indicates existing conditions in proportion to the degree of completeness of 

 collections. That part of taxonomy which relates to the classification of existing forms 

 considers the relations of these forms to each other as shown by structural characters 

 alone. In the study of the relationship of existing forms there is tendency to endeavor to 

 account for the origin of some existing species in other existing species. 



Jordan (1905a, p. 293) wrote: 'Where species can readily migrate, their uniformity is 

 preserved; but whenever a form becomes localized its representatives assume some 

 characters not shared by the species as a whole. When we can trace, as we often can, the 

 disappearance b}' degrees of these characters, such forms no longer represent to us 

 distinct species. In cases where the connecting forms are extinct, or at least not repre- 

 sented in collections, each form which is apparently different must be regarded as a 

 distinct species.' 



From the foregoing it would seem that the statements regarding the 'disappearance 

 by degrees' of characters and the extinction of connecting forms refer to present space 

 and not past time. At any rate, the statement is based upon existing situations. There 

 are geographically intergrading forms with terminals more or less different from each 

 other. There are widely different forms with no geographical intergrading forms. There 

 are closely related forms more or less geographically separated and having no inter- 

 grading forms, and there are geographically and structurally distinct forms with in- 

 direct irregularly geograpliical intermediates that do not constitute intergradation. 

 Satisfactorily to apply the usual taxonomic methods to all of these conditions involves 

 certain difficulties, wliich have caused considerable confusion and lack of uniformity 

 and consistency in nomenclature, particularly of the Salmonidse. Efforts to regulate 

 these conditions have resulted in the adoption, by some ichthyological authorities^, 

 of arbitrary rules, to the effect that if one form differs from others by constant characters, 

 however great or small, the form must be considered as a distinct species; the known 

 existence of geographical intergradation of structural characters, would according to 

 priority of description, make one or the other terminal a subspecies. This rule permits 

 the intermediate forms of the last category mentioned to be regarded as distinct species, 



'Jordan and Evermann in MS. 



