BOYCOTT : THE RADULA OF HYAI.INIA. 303 



Anatomically I could find no very important differences. To say 

 that they would have been demonstrated if the whole of the organs 

 had been examined quantitatively as has the radula, is to express a 

 mere opinion. The only point to which attention should be drawn 

 is the exceptional length of the penis in the Bicknor specimens. 

 This is shown in the figure which gives camera lucida outlines of the 

 lower parts of the genitalia of two specimens from each locality, 

 all prepared in the same way from shells between 8 and 9 mm. in 

 diameter and magnified to the same degree. To the other differences 

 shown in the figures I should attach no importance. 



We have then here specimens of Hyalinia helvetica from four 

 widely separated localities. Each series has some rather ill-marked 

 shell characters and some well-marked radular characters, and it 

 would be consonant with one attitude towards such problems to 

 elevate some or all of them to nominal rank. Such a course has the 

 clear and definite advantage that it would focus attention, controversial 

 or acquisitive, upon the group and thus lead pretty quickly to a 

 desirable amplification of our knowledge. But before taking such a 

 step further information is wanted along three lines — (i) As to 

 whether helvetica from any two localities are identical when judged 

 by the criteria here adopted. (2) Whether the variation here 

 described is local or familial. As it happens each series was collected 

 from a very circumscribed locality, a good deal less than fifty yards 

 square in every case. The results, therefore, do not throw any light 

 on the question whether, e.g.^ the Marple individuals are fairly repre- 

 sentative of the helvetica living in the Marple valley or whether their 

 characteristics are confined to the particular colony from which they 

 came.^ It is a common habit of helvetica to live in rather definite 

 colonies, like lucida, and not with the general dispersion of cellaria or 

 nitidula, and this mode of occurrence (which, by the way, does not 

 hold at all in the Banstead district of Surrey) is, perhaps, provocative 

 of the development of local characters. (3) Whether the character- 

 istics found are permanent in the sense that they continue unaltered 

 in any one colony over a period of years. Whatever the answer to 

 these questions may be, it is obvious that radular characters may prove 

 of considerable value in the differentiation of local races and that 

 local variation in the radula must be taken into account in the 

 consideration of " specific differences." 



Summary. 

 The radul^e of Hy. helvetica from four localities (Surrey, Gloucester- 

 shire, -Cheshire and Carnarvonshire) are described and found to have 

 characteristic features in each case. 



I The specimens dealt with here came from the well-known spot by the acqueduct to which 

 Mr- St£nden directed my attention. 



