xii PREFACE. 



I have followed the author of ' British Conchology ' 

 in the method of arrangement as well as in the 

 nomenclature which he has adopted. A long list of 

 synonyms would have increased the size as well as 

 the expense of the book, and the sight of it might 

 have injuriously affected the nervous system of the 

 reader. I have therefore refrained from giving one. 

 In selecting the shells for illustration, I endeavoured 

 to make choice of specimens which would, as nearly 

 as possible, represent the usual or typical form and 

 size ; in one or two instances, however, I was unable 

 to do so. The figures of both species of Physa are 

 less, and those of Limnaa stagnalis rather larger than 

 specimens of the usual size. As the camera was 

 adjusted so as to produce photographs of the actual 

 size of the shells, I deemed it unnecessary in describing 

 each species to give its dimensions. 



The shells of Paludina contecta and P. vivipara, 

 which should have been figured on Plate IV., so as to 

 show the apertures, were accidentally broken at the 

 moment the sensitive plate was being placed in the 

 camera. Figures of those species, showing the oper- 

 cula, have therefore been given on Plate IX. 



It only now remains for me to express my best 

 thanks to those who have so kindly assisted me in 

 this my self-imposed and pleasurable task. To my 

 friends Dr. Gwyn Jeffreys, Mr. Ponsonby, the Rev. J. 

 McMurtrie, and Mr. H. Groves, I am indebted for the 

 loan of some of the rarer species, as well as for other 

 kindly aid. To Mr. Groves my special thanks are 

 due for the admirable enlargements of all the British 



