GENERAL, DISCUSSION 17 



whicn probably cross it, making a probable total British Colum- 

 bian fauna of one hundred and thirteen forms. Considering 

 the very small area occupied by this assembly, when compared 

 with the vast expanse populated by the Canadian fauna, the 

 number is notable. Doubtless in both cases future exploration 

 will add a reasonable number not now enumerated or still 

 undescribed by naturalists. 



The contributions from the Columbian assembly to the fauna 

 of Alaska south of the Alaskan and west of the Cascade Ranges 

 comprise thirty five known and six probable species, a total of 

 forty one forms probably inhabiting the area referred to. Some 

 of these, however, are common to northern Alaska also, making 

 the proper deduction for which we find sixty five species of land 

 and fresh water mollusks known to inhabit the territory of 

 Alaska, with six or seven more which are likely with further 

 exploration to be credited to it in addition to those now known, 

 even if no undescribed species turn up. 



The vast unexplored areas, the uncertainties connected with 

 lists of obsolete names and doubtful identifications, the doubt 

 as to what may be considered specific limits in groups of noto- 

 rious variability, and especially the frequent absence of specimens 

 from which better deductions might have been drawn than were 

 possible from the extant literature, have all contributed to the 

 difficulties under which this memoir has been prepared. Those 

 who have done work on similar lines will understand, and will 

 view without undue severity, the imperfections which the author 

 only too well realizes, and yet which it was out of his power, 

 in the present state of our knowledge, to avoid. It is hoped, 

 however, that this summary will make the path somewhat easier 

 for those who follow him, and contribute a reasonable share to 

 the better appreciation of the facts of Nature of which it treats. 

 And if, among the hardy explorers of whom our neighbors of 

 Canada are justly proud, this paper serves to stimulate an 

 increased interest in the subject, the author will feel that his 

 endeavors are amply repaid. 



