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PRESIDENTIAL ADDRESS. 

 By G. K. GuDE, F.Z.S. 

 Delivered 13iA Febrxianj, 1920. 

 THE ARMATURE OP LAND MOLLUSCA. 

 The subject on wMch I venture to address you to-night has been 

 a favourite study with me for a considerable number of years. My 

 interest in these structures was first aroused through the receipt 

 of some specimens of Gorilla from Ceylon, on which I based a new 

 species. The Editor of Science Gossij) having in 1896 requested 

 me to contribute some articles on MoUusca, I chose the " Armature 

 of Helicoid Land Shells " as my subject, which, however, was side- 

 tracked into what amounts practically to a monograph of the genera 

 Corilla and Plectopylis. 



On that occasion I drew attention to the fact " that Mollusca have 

 numerous enemies is well known to naturalists, for not only do they 

 serve as food for many mammals, birds, and reptiles, but they are 

 preyed upon by some insects, and eveil by other mollusca. Naked 

 slugs are especially exposed to the attacks of birds, slow-worms, and 

 snail-slugs {Testacella), and, in foreign countries, of carnivorous 

 snails, such as Glandina and others. Shell-bearing Mollusca likewise 

 are devoured by birds and mammals ; they have besides many insect 

 enemies, ^particularly in tropical climates, and we shall, therefore, 

 not be surjDrised to find that in several instances these creatures have 

 come to be jDrovided with special means of protection. This has 

 been attained in various ways, indirectly by protective resemblance 

 between the forms or colours of the shells and their immediate sur- 

 roundings ; or directly by special structures, such as teeth, plates, 

 or constrictions, serving as buttresses or barricades behind which 

 the animal can withdraw. It is probable, however, that these 

 structures may at the same time help to strengthen and support the 

 outer wall of the shell ". 



That structures of this nature serve as a means' of defence against 

 the attacks of carnivorous insects and similar creatures was suggested 

 as long ago as 1829 by Guilding,^ who, in speaking of the teeth and 

 laminae of the Pupidae, observed that " they may answer the purpose 

 of an operculum to keep out enemies, while they afiord no obstacle 

 to the motion of the soft and yielding body of the animal ". 



Of much interest in this connection is a note by Lieut. -Col. Godwin- 

 Austen, who, in a paper on the genus Plectopylis, states that " when 

 breaking up a number of shells to expose the barriers and ascertain 

 if their characters were constant, I was greatly interested to find in 

 two instances the presence of small insects that had become fixed 

 between the teeth ".^ 



1 Zool. Journ., vol. iv, 1829, p. 168. 



2 Proc. Zool. Soc, 1874, p. 611. 



