264 PEOCEEDINGS OF THE MALACOLOGICAL SOCIETY. 



the fact of the ditch in hot weather nearly drying up, might canse 

 alteration in the direction of shell, if it be in process of formation. 

 This idea was hinted at by Jeffreys many years agx). Fortunately, 

 however, Standen ^ made a careful examination of these forms, keeping 

 them in an aquarium, and he found that all the distorted shells were 

 covered with a luxuriant growth of Epidylis anastaticn, one of the 

 rigid-stalked Vorticellce, whereas from the parts of the ditch lacking 

 abnormalities the shells were clean and clear. This appears to be the 

 probable cause, the animal shrinking when forming its shell from 

 contact with the Vorticellce. 



While on the subject of these distorted forms I may recall a veiy 

 interesting series of Littorina rudis, var. tcnebrosa, noticed by myself,* 

 from the Fleet Backwater near "Weymouth. They were picked up, 

 dead shells only being found, in quantity on the shore, and were 

 perhaps killed by a cold spell which had occurred. I doubtfully 

 referred then to the possible cause as being attached weed which the 

 animal was endeavouring to avoid, and in the light of Standen's 

 investigation further enquiry there seems very desirable. 



Aulopoma, scalarilorm, from Ceylon. 



Akin to these forms of Planorhis is the elevation or depression of 

 the spire. Helix pomatia, for example, has been seen so depressed as 

 to be planorbiform,^ while the scalariform specimens are well known. 

 Enquirj- will probably show that this elevation or depression is 

 correlated with some peculiarity of the animal. Baker* has recently 

 observed, after taking measurements of a large number, that in 

 Pyramidula alternata the western specimens have a higher shell than 

 the eastern, and vary more in spire elevation. In the Island of Syra ® 

 it has been recorded that of Pyramidula rupestris more scalaroid than 

 normal shells occur, and the theory has been put forward that, under 

 some peculiar condition, a new race may be developing. "Welch ^ has 

 illustrated some interesting scalariform and distorted specimens of 

 Helix nemoralis from the sand-dunes of Bundoran, and suggests that 

 the distortion may be due to "the intrusion of a grain of sand during 

 the early life of the moUusk, and the consequent deviation of the 

 whorl from its normal course of growth." It is needless to go 



' Journ, Conch., vol. ix, p. 216. 



2 Proc. Dorset Club, vol. xiii (1892), pp. 191-198, one plate. 



2 Bellevoye: Bull. Soc. Rheims, vol. viii, p. 89. 



* Amer. Nat., vol. xxxviii, p. 667. 



5 Nachrbl. Deutsch. Malak. Ges., 1880, p. 07. 



'' Journ. Conch., vol. x, p. 244. 



