2S2 



ON VARIATION IN THE RADUL^ OF CERTAIN: 

 BUCCINID^. 



By M. V. LEBOUR, B.Sc. 



(Read before the Society, November 8th, 1905). 



^Plate VI. 



Variation in the radula is by no means uncommon m Gastropods. 

 This has been chiefly investigated in Bucciniim and its aUied genera, 

 many species being easily obtainable. The organ in these cases is 

 simple and large enough to be readily seen, consisting of a long 

 ribbon bearing many rows of chitinous teeth. In the Buccinidse, 

 FasciolariidcC, and others, there is a central plate and one lateral on 

 each side, and these are divided into teeth, which are usually regular 

 throughout the radula. It is the number of these teeth which varies 

 very considerably, both in centrals and laterals, but in the former 

 much more frequently than in the latter. 



Bateson, in his " Materials for the Study of Variation," p. 262, 

 draws attention to Friele's work on Bucciiiu/n, and also refers to 

 information given him by the Rev. A. H. Cooke on this subject. 

 Friele has worked thoroughly on the radula of the Norwegian species 

 of the genus Bucciniim (^Jahrb. Deutsch. Mai. Ges., vol. 6, p. 257, 

 1879). In a most elaborate paper he shows how enormously the 

 radula of Biiccinuvi undatuvi varies, and also, in a similar way, other 

 species of the same genus. He regards the radula as of little value 

 for the identification of species in comparison with external characters; 

 closely-allied species, or what authorities have taken to be separate 

 species, not presenting definite differences in the radula. Even in 

 what we take to be distinct genera, we find sometimes that the forms 

 of the radulae merge into each other. For instance, the typical radula 

 in Bucciniim iindatum has in each row a central plate bearing six 

 teeth and a lateral plate on each side bearing four teeth. The typical 

 form of Neptunea anttqua has a central plate bearing three teeth and 

 a lateral plate on each side bearing three teeth. Now, Bateson gives 

 in his notes above mentioned a figure of a radula of Buccittmn 

 undatiim, from Labrador, from the collection of the Rev. A. H. 

 Cooke, having three centrals and three laterals on each side through- 

 out, these showing the same form as the typical Neptunea a?itiqua. 

 This certainly is a very unusual specimen, although Buccinuin is 

 extremely variable. 



Having had exceptional opportunities in the laboratory of Arm- 

 strong College', Newcastle-upon-Tyne, of examining the radula of 

 Bucciniim undatiim^ Neptunea antiqua, and (with fewer specimens) 

 Volutopsis nofvegicus, and Biicccinofusus ber/iiciensis, I think the results 



