379 



OX THE EADUL^ OF THE BRITISH HELICIDS. (Part III.) 

 By Kev. E. W. Bowell, M.A. 



Read llth June, 1909. 



Thk radulee to be described in the present paper are those of vtr^^ 

 cantiana, revelata, sericea, hispida, rufescens, caperata, Itala, harbara, 

 and granulata. Generic names will not be mentioned for the present ; 

 and to avoid confusion the species will be mentioned in the above 

 order, which is the result of a classification of the peculiarities of 

 the radulse. 



On p. 126 of Volume VIII of these "Proceedings" I stated that 

 barhara differed from the other small Helices of this group in the 

 possession of bifid marginal mesocones. Closer examination of better 

 mounted specimens has shown that this character also is found in 

 eaperata, Itala, and granulata ; this will be noted in the accompanying 

 illustrations. This correction is of great importance, since it appears 

 probable that the species possessing this character are nearer to the 

 larger Helices than to those in which it is not present. By the term 

 ' larger Helices ' I mean the species described in Part II of these 

 notes, purposely using an unscientific phrase, because the limits of 

 this group are very vague to me at present. The study of this 

 particular point has emphasised an opinion towards which I have 

 inclined for a long time, namely, that size has counted for too much 

 in our systems of classification. I was led to look out for large 

 species which might be supposed to be magnified races derived from 

 known smaller species ; and also for small species which appear to be 

 the starved representatives of larger ancestors. Instances of this kind 

 of thing are not rare amongst insects, but probably there is no part of 

 the animal kingdom where they are more frequent than in that to 

 which our studies are devoted. On examining these pairs of forms we 

 do not find that they are ever the exact counterparts of each other; 

 and the same is true of large and small races occurring in the same 

 species. Increase of size or diminution of size involve in every case 

 a redistribution of symmetry, because the constituent cells of the 

 organism do not share the increase or diminution. In the case of 

 some organs it matters more, and in the case of other organs it matters 

 less, that the general scale of the organism should be increased or 

 diminished. The radula appears to be an organ that does not readily 

 vary in size with the general scale of the organism. It has already 

 been pointed out that in our British Helicidse the size of the radula is 

 not proportionate to the size of the animal, though the proportion 

 it bears is closer than in some other groups. This is true also of 

 the individual unci. But the individual unci of Zonites Algiriis are 

 not larger than those of Vitrea lucida, consequently there must be, 

 and there are, many more of them. And since the number of unci is 

 multiplied, their form is altered ; they are simplified so that the 

 admedians resemble Helicid admedians in general appearance. If we 



