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THE DISPERSAL OP LAND SHELLS BY THE AGENCY OF MAN. 

 By Lieut.-Colonel H. H. Godwin-Austen, F.R.S. 



Read 12th June, 1908. 



During the past year some interesting cases of shell dispersal have 

 come to my notice, which I think are worth placing on record. 



In June, 1905, I read a paper before this Society on "The 

 Extension of the genus Macrochlamys to the Island of Mauritius," 

 based on specimens collected and sent to me by Monsieur E, Dupont, 

 of that island. There were two species — one (A) in its shell, having 

 a very short right shell-lobe, the other (B) only the animal, no shell 

 [vide Proc. Malac. Soc, vol. vi, pi, xviii, figs, i and vii respectively). 

 The form of the left shell-lobe also differed in the two species 

 (figs, ii and vi). The species A was dissected and its anatomy found 

 to be in every respect similar to the typical Indian species of the 

 genus. I could not, however, at the time match the shell with any 

 species known to me and in my collection at that date. 



Since then I have received, through the kindness of Mr. F. Ede, of 

 Silchar, Cachar, Assam, a number of species, preserved beautifully in 

 spirit, found in that district, and among them is a shell which tallies 

 exactly with the Mauritian one in form, colour, and sculpture. The 

 only difference I notice lies in the colour of the animals, those from 

 Cachar being extremely colourless, not gray ; but this may be due 

 to the alcohol having bleached the animals. This Cachar shell is an 

 undescribed form or variety of Macrochlamys indica of Calcutta. 



I think we may assume the two species to be identical, and 

 that the home of the Mauritian shell was Cachar. The manner of its 

 transit I believe to be as follows : — There is a very numerous Hindustani 

 population in the Mauritius, and a large proportion of them are rice- 

 eaters. In the districts of Sylhet and Cachar the principal cultivation 

 is rice, which is exported in boats, almost direct from the threshing- 

 floors near the villages in the form of dhan, i.e. the unhusked grain. 

 The large grain-boats drop down the River Soorma to the Brahmaputra, 

 and on to Calcutta or Chittagong, their cargoes to be finally shipped in 

 steamers and native sailing craft to the Mauritius and other places. 

 "While the unhusked rice is lying on the threshing-floors, open to the 

 air, there is nothing to prevent these snails and fertile eggs getting 

 mixed up in the grain and retaining their vitality until turned out 

 upon the floors of the grain-yards in the Mauritius or elsewhere, and 

 in sufficient numbers to become established, particularly as the 

 threshing-places have frequently plantain-trees growing near them, 

 a favourite haunt of species of Macrochlamys. The time of transit 

 would not be very long, and the dhan would be sufficiently damp to 

 keep them alive. 



The dispersal of our common slugs to many parts of the world is 

 well known ; they make themselves quite at home at the Cape, in 

 Australia, and the Mascarene Islands. Among a collection of shells 

 in spirits sent me by Mons. E. Dupont, was a tube of slugs. On 



