28 JOURNAL OF CONCHOLOGY, VOL. 12, NO. I, JANUARY, I907, 



open to discussion is wliich standard affords the greatest opportunities 

 for advantageous practical work. On the one hand there is the 

 danger of losing sight of the close relationship existing between a 

 number of forms by placing them separately as species amongst 

 other and heterogeneous forms, whilst by grouping them as varieties 

 of a single species we adopt a more cumbrous nomenclature. 



Before leaving the subject ot species I may point out that a very 

 artificial system of separating species by adopting a wholly arbitrary 

 standard was suggested by Edward Forbes and resuscitated by 

 Bourguignat. It is that forms having constantly distinct characters 

 are to be considered distinct, specifically provided that these distinct 

 characters are not less than three in number. The folly of such 

 a system was pointed out by Jeffreys, who commented on it as 

 follows : — " it is notorious that the relative value and constancy 

 of these characters have yet to be determined, and that there is 

 no standard of reference by which naturalists can be guided in 

 adjudging some forms to be species and others to be varieties in 

 different genera." 



I have incidentally referred to variation, and the time has now 

 come for me to define a variety. A variety is a group of individuals 

 which differs from the typical or normal form in more or less distinct 

 characters which are transmissible to the offspring. These distinct- 

 ive characters often though not invariably merge by insensible 

 gradations into those of the type or of another variety : but some- 

 times the varietal form is found only in some special locality, where 

 the type does not occur. When varieties are quite local and well 

 marked they constitute a race or sub-species. 



It is very necessary to emphasize the fact that variation affects not 

 only the shells of moUusca but the soft parts as well. Year by year 

 we are gaining a greater knowledge of the variation in the number 

 and arrangement of the radular teeth. Consequently the mere fact 

 that a certain amount of difference is observed in the anatomy of 

 two forms by no means warrants any assumption that the two forms 

 are specifically distinct. In addition to varieties proper there are 

 several kinds of departure from the typical form that require 

 mention. 



Monstrosity is a term generally applied in a very loose way by 

 conchologists, although the term has really a very definite signifi- 

 cance. A monstrous form is one in which the characteristic 

 peculiarity always appears during the embryonic stages of existence, 

 and which is due to an altogether extraordinary or perverted course 

 taken during the developmental processes. Reversion of the normal 

 direction of the spiral growth in gastropods is of course the best 

 known example. In early embryonic life the parts are bilaterally 



