PISIDIUM. 19 



is, honestly and to the best of one's ability carefully to 

 work out the subject and to submit the result to the 

 free criticism of other naturalists. This last course I 

 have endeavoured to pursue ; and I shall not feel in the 

 least degree mortified or discouraged if the conclusions I 

 have arrived at, with much pains and great hesitation, 

 are not accepted by all my scientific brethren. 



To give some idea of the labour involved in this in- 

 vestigation, I may mention that my own cabinet con- 

 tains no less than 274 parcels of Pisidia, which have 

 been, in the course of the last thirty or forty years, col- 

 lected from different localities and sources, and comprise 

 many thousands of specimens ; that I have personally 

 examined the types of those species which have been de- 

 scribed by Dr. Turton, Mr. Jenyns, Mr. Alder, Dr. Bau- 

 don, and other conchologists who have published on the 

 subject ; that I have collected these tiny shells in many 

 parts of Holland, Germany, France, Switzerland, and 

 Italy, for the sake of comparison with British forms ; 

 and that I have had to refer to numerous works in many 

 languages in order to collate the descriptions of forty- 

 one different species which have been proposed by Euro- 

 pean writers within the last century. Of these, I cannot 

 conscientiously recognize more than six as distinct. 



It will be convenient to divide the British species, 

 which are five in number, according to their shape, as 

 follows : 



A. Triangular. 1. P. amnicum. 2. P. fontinale. 



B. Oval. 3. P. pusillum. 



C. Round. 4. P. nitidum. 



D. Oblong. 5. P. roseum. 



