290 TAYLOR : ON THE VARIATION OF MOLLUSCA. 



tion. In addition, I also propose to endeavour to show some 

 reasons why it is desirable to bestow — or retain if already bes- 

 towed — definite names on the more important deviations from 

 what I may term the central form. 



In this view I have the support of one of the most eminent 

 and experienced conchologists of the day, Prof. Ed. v. Martens, 

 who says, " It is certainly desirable that every local form, well- 

 marked zoologically or geographically, should have a distinct 

 name." Dr. Jeffreys also says, " Systems of classification are 

 as indispensable to a naturalist as tools to a workman. This 

 necessity of science equally applies to the discussion of the 

 interesting question as to the origin and mutability of species, 

 which in the absence of such data could not be satisfactorily con- 

 ducted." Moquin-Tandon, Forbes and Hanley, Jeffreys, and 

 almost every author of repute who has attempted to deal with 

 his subject in a thorough and efficient manner, has adopted the 

 principle of applying definite names to the most important or 

 interesting variations. 



But before proceeding further, it will be advisable to con- 

 sider briefly what is the difference between a species and a 

 variety. Dr. Gwyn Jeffreys, than whom we can hardly have a 

 better conchological guide, says, " It is undeniable that certain 

 definite forms, called species, exist, and that they constitute 

 more or less extensive groups of individuals, which resemble 

 each other as well as their parents and offspring, to the same 

 extent that we observe in the case of our own kind. These 

 groups to deserve the name of species must be distinct from 

 others ; because if any of them are so intimately blended to- 

 gether by intermediate links as to make the line of separation 

 too critical, the test fails, and a subordinate group, or what is 

 called a ' variety ' is the result." This is undoubtedly an 

 excellent and satisfactory definition as far as it goes, but I would 

 add to it, as a basis, the necessity of structural difference in the 

 organization of the animal, for the permanent retention of specific 

 rank. I am aware that Jeffreys has said, " that the body or soft 



J.C, v., April, 1888. 



