SHOWERS OF SHELLS 



47 



Writing to the Zoological Society of London from New 

 Caledonia, Mr. E. L. Layard remarks : ^ " The West Indian 

 species Stenogyra oetona has suddenly turned up here in thou- 

 sands; how introduced, none can tell. They are on a coffee 

 estate at Kanala on the east coast. I have made inquiries, 

 and cannot find that the planter ever had seed coffee from the 

 West Indies. All he planted came from Bombay, and it would 

 be interesting to find out whether the species has appeared there 

 also." 



Sometimes a very small event is sufficient to disturb the 

 natural equilibrium of a locality, and to become the cause either 

 of the introduction or of the destruction of a species. In 1883 

 a colony of Helix sericea occupied a portion of a hedge bottom 

 twenty yards long near Newark. It scarcely occurred outside 

 this limit, but within it was very plentiful, living in company 

 with IT. nemoralis, H. hortensis^ H. hispida, R. rotundata^ Hyalinia 

 cellaria and Hy. nitidula^ and Cochlicopa luhrica. In 1888 the 

 hedge was well trimmed, but the bottom was not touched, and 

 the next year a long and careful search was required to find 

 even six specimens of the sericea? 



Showers of Shells. — Helix virgata^ H. caperata^ and Cochli- 

 cella acuta sometimes occur on downs near our sea-coasts in such 

 extraordinary profusion, that their sudden appearance out of 

 their hiding-places at the roots of the herbage after a shower of 

 rain has led to the belief, amongst credulous people, that they 

 have actually descended with the rain. There seems, however, 

 no reason to doubt that MoUusca may be caught up by whirl- 

 winds into the air and subsequentl}^ deposited at some consid- 

 erable distance from their original habitat, in the same way as 

 frogs and fishes. A very recent instance of such a phenomenon 

 occurred ^ at Paderborn, in Westphalia, where, on 9th August 

 1892, a yellowish cloud suddenly attracted attention from its 

 colour and the rapidity of its motion. In a few moments it 

 burst, with thunder and a torrential rain, and immediately after- 

 wards the pavements were found to be covered with numbers 

 of Anodonta anatina, all of which had the shell broken by the 

 violence of the fall. It was clearly established that the shells 



1 P. Z. S. 1888, p. 358. 2 w. A. Gain, Naturalist, 1889, p. 58. 



3 Das Wetter, Dec. 1892. Another case is recorded in Amer. Nat. iii. p. 

 556. 



