TAYLOR : ON THE VARIATION OF MOLLUSCA. 303 



This explanation does not account for the distortions which 

 are also occasionally irregularly spiral, and which have been 

 found in warm water reservoirs, and in streams of water pumped 

 from the coal pits in Yorkshire and elsewhere, these may be the 

 result of the unhealthy and unnatural conditions under which 

 they live. 



Even from the few foregoing illustrations and my introduc- 

 tory remarks, it will be seen how variable our species are and 

 what complex forces are ever acting upon them, and producing 

 more or less marked modifications. I regret that the time at 

 my disposal does not allow me to discuss more than one or two 

 points, or I should wish to have laid before you the results of the 

 observations of some of our most observant scientists, on the 

 influence upon their molluscan inhabitants, of brackish water, of 

 turbulent and agitated streams and lakes, and also of deep and 

 still water. Decollation, erosion and some of the alleged causes 

 of several peculiarities and deformities amongst our land and 

 freshwater shells would also have merited and received atten- 

 tion. 



If my views of species are correct, what immense assistance 

 the biologists could render us in striving to arrive at a true 

 knowledge of specific and varietal limits in the moUusca. It is 

 however to be sincerely regretted that we cannot hope for much 

 help at present, as many even of the most eminent biologists of 

 our own country, do not place any, or very slight value upon 

 precise specific identification, thus the work of some of our most 

 celebrated men loses much of its value from what I feel com- 

 pelled to consider their reprehensible carelessness in not securing 

 an exact determination of the specimens they have under exami- 

 nation, and which specific uncertainty often renders it necessary 

 that their observations should be repeated and confirmed by 

 others more mindful of specific differences before the informa- 

 tion they have given can be fully utilised and receive the 

 consideration its merits otherwise would demand. 



