X INTRODUCTORY NOTE. 



gratefully acknowledged ; to Mr. Robert Standen and 

 Mr. J. Ray Hardy he is under obligation for many 

 striking facts and the loan of specimens, to Mr. G. K. 

 Gude and Mr. R. W. Goulding for the preparation of 

 several translations, and to Mr. C. T. Musson for per- 

 mission to use a manuscript work on the " Land and 

 Fresh-water Shells of Nottinghamshire," containing 

 excellent essays on local distribution and means of 

 dispersal. 



To Dr. Alfred Russel Wallace, who, with great kind- 

 ness, has looked over the proofs and contributed the 

 foregoing preface, the writer owes a special and 

 irredeemable debt of gratitude. 



With a view to the collection of further facts illustrat- 

 ing the means of dispersal possessed by molluscs and 

 allied animals. Dr. Wallace has suggested that the 

 writer should invite " naturalists and sportsmen in all 

 parts of the world " to co-operate by furnishing notes 

 of, or references to, observations which they may have 

 made or recorded, or which they may be able to make 

 or record in the future. Many persons, both at home 

 and abroad, he imagines, would make observations " if 

 they knew what was wanted, and had the address of some 

 one who would appreciate and use them." It may be 

 mentioned that, amongst other things, the examination of 

 large numbers of floating trees, etc., encountered upon the 

 ocean, and of drift-timber and brushwood found stranded 

 upon the coast-line, would possibly be productive of 

 surprising results, as also would the careful and system- 

 atic inspection of the feet and feathers of birds shot 



