780 REPORT OF COMMISSIONER OF FISH AND FISHERIES. 



while others are simple lists of species, to a great degree dependent 

 for their value on the reputation of their anthors for knowledge and 

 reliabilit3\ 



DOUBTFUL SPECIES. 



The nanes of many of the species are still very unsettled or require 

 confirmation. The doubts arise principally from two sources : 



1. Erroneous identification with previously-described species. 



2. Erroneous differentiation from previously-described species. 

 Both categories of errors mostly result from two causes : 



1. From default of actual comparison of specimens representing the 

 different forms. 



2. From erroneous valuation of certain similarities or differences 

 which maj^ exist between the respective forms; in some cases {a) the 

 differential characters having been overlooked or subordinated to the 

 common characters, while in others (h) differences which may be ob- 

 served on comparison of isolated specimens are not confirmed by larger 

 series, or fail to apply to forms from intermediate regions. 



As might be expected from these considerations, the doubts affect 

 chiefly (1) the species found in the temperate or arctic regions, and 

 which are represented by forms in both hemispheres ; and (2) those of 

 large size, represented also in both hemispheres, or inhabitants of the 

 open sea. 



The author has not at present the means to solve all these doubts for 

 others or to satisfy himself. While the material for the American forms 

 is often ample, that for the Enropean or exotic types (chiefly in the 

 case of the large sharks, rays, and scombroids) is, in several cases, in- 

 sufficient. Therefore he has preferred to retain the names given to the 

 American forms as distinct species, although he is inclined to believe 

 that they will be eventually fonnd to be co-specific with other forms. 

 For the guidance of others, these doubtful forms are indicated in the 

 following catalogue, the nature of the doubt being distingnished, whether 

 referring to the more or less dubious distinction of the nominal species, 

 {d. s.,) or whether to the dubious identification of the form with another, 

 {d. <a) s.) Although these stigmas are cast on a number of the names 

 admitted, it is not probable that future comparisons will necessitate 

 changes for most or even a large proportion. N'evertheless, the desira- 

 bility of a settlement of the doubts one way or the other is not the less 

 decided. 



The opportunity for the settlement of some of these questions at least 

 will, however, soon be furnished, as specimens of the desirable species 

 have already been promised, or are on their way from Europe, and iu a 

 future report the results of the comparisons may be made known. To 

 the efforts of the Commissioner of Fisheries we have been indebted for 

 the means of determining some of the doubtful questions earlier than 

 would otherwise have been possible, and we will soon have the means 



