PREFACE, 



THE present volume is based on the studies made by the author 

 in his private time during nine winter sessions. It. deals with 

 the collections of recent and fossil shells, belonging to the genus 

 Pisidium, in the British Museum (Natural History). It is, how- 

 ever, by no means restricted to these, since Mr. B. B. Woodward 

 has had the advantage of making use of a large number of 

 specimens derived from other sources. This is indicated by the 

 unusually long list of helpers whose assistance he acknowledges 

 in his Introduction, and to whom the thanks of the Trustees 

 are also due. 



The difficulty of the work has been increased by the small size 

 of the shells described. 



The Catalogue is in one respect a departure from the usual 

 practice of the Museum, since it deals with the collections of two 

 Departments, represented respectively by the recent and by the 

 fossil forms. 



SIDNEY F. HARMER, 



Keeper of Zoology. 

 Briti3h Mupeum (Natural History), 

 London, S.W. 

 March 7, 1913. 



