1892.] 



THE BRITISH NATURALIST. 



47 



As regards decollation, I am enabled to add Limnaea tnmcatida to 

 the British list on the authority of Mr. W. E. CoUinge. He also 

 confirms me as to the bleaching of the apex in Clausilia — in the case 

 of C. rugosa at Ingleton, and C. laminata at Wetherby. Moquin- 

 Tandon mentions Clausilia, Cyclostoma, and Linmaea as the French 

 genera in which decollation occurs, and also records the occurrence of 

 a colony of Planovbis vortex, in which each shell had a little hole through 

 the centre, where the first whorl ought to have been. I should of 

 course have already mentioned Cyclostoma elegans as another frequently 

 decollate shell. Many of the foreign forms of this genus and of its 

 allies, such as Tudora, Adamsiella, and Pomatias, habitually lose the 

 the apex of their shells in maturity. Cylindrella, with nearly 200 

 species is a good instance of an liabitually decollate genus; while 

 Pirena., Telescopium, and Cerithidea are usually the same, but may be 

 obtained faultless in favourable localities, — the loss of apex depending, 

 (as in all aquatic genera) on the character of the water. This 

 influence seems especially to affect estuarine species, which live on 

 muddy flats and are subject to the changes of tide. Take the genus 

 Hydrobia, essentially a native of brackish water; oi H. ventvosa there is 

 a var. decollata chronicled in Jeff'reys, while we have received from 

 Canon Norman a var. truncata Norm, of H. itlvae from Brodick 

 essentially similar in characteristics. 



Dr. Sterki, the American authority on Pupa, has just been 

 turning his attention to our little friend Helix piilcliella and 

 its forms. He is a firm believer in the specific validity of what 

 we know as var. costatsi. Now that this point has been revived, it 

 will be well for English collectors to give the results of their 

 experience. Dr. Sterki says that he can recognise a costata even 

 when ribless, by the depression of its spire and the more rapidly 

 increasing whorls. Comparison of series from the same locality 

 would be most valuable and we urge collectors who have the 

 opportunity, to corroborate or refute the value of these characteristics. 



Limax agvestis, L., put in appearance about 7 years ago on the 

 Pacific coast of North America, and is now as great a garden pest as 

 with us. It is especially flourishing in San Francisco and Victoria, 

 B.C. — B. ToMLiN, The Green, Llandaff. 



On the Variation in the Banding of Helix. — The subject of 

 band-variation in the various species of Helix has for a considerable 

 time occupied the attention of naturalists, and yet -our knowledge 

 of the cause or causes that give rise to such a multiplicity of forms is 

 very deficient. It seems to me that the collecting of these variations 

 will add very little to our knowledge, certainly a good result has been 



