DISPERSAL BY MAN. 179 



in 14 1 8, sea-girt, and less than 400 square miles in 

 area, possess, according to the Rev. Dr. Watson, no less 

 than thirteen kinds of molluscs (six slugs and seven 

 land and fresh-water shells), believed to have been 

 introduced by man, and now well-naturalized, namely : — 

 Avion ater^ Liniax gaoates, L. inaxiinus, L. flavus, L. 

 agrestis, Testacella inaugei, Hyalinia cellar ia, Helix 

 pulchella, Buliiiius decollatiis, B, ventricosus^ Cochlicopa 

 liibrica, Liiinicea acicta, and ^' Ancylns striatus Q. and 

 G. " ; and there are also six other similarly introduced 

 kinds — Testacella Jialiotidea^ Helix aspersa, H. rottindata^ 

 Planorbis glaber, PJiysa acuta, and Hydrobia siinilis — 

 much more recently imported, and hardly to be 

 regarded as truly naturalized.^ Snails thus introduced, 

 as it is interesting to note, often increase with surprising 

 rapidity ; it is notoriously dangerous, indeed, to turn 

 out any creature in a new country, where its enemies are 

 possibly absent, and the truth of this has been sorrowfully 

 enforced in some of our own colonies. The European 

 Hyalinia cellaria, it is said, occurs literally in hundreds 

 in the space of a few square feet near a water- fall in St. 

 Helena; the British Cemetery at Buenos Ayres, 

 according to a recent report, is "overloaded with 

 Helix poinatia ; " our common garden snail {Helix 

 aspersa),m\xoA\xQ.^(^ into the Cape apparently within the 

 memory of a living naturalist, is there astonishingly 

 prolific; Mr. J. S. Gibbons, in 1878, mentioned that he 

 had nowhere seen it in such plenty as near Cape 



R. B. Watson, " Journ of Conch.," vii. (1892), pp. 1-3. 

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