Reviews — B.B. Woochvard — British Species of Pisidium. 83 



shell would be more useful to the reader in the text of the chapter 

 on Classification to show the topography of the shell, although well 

 illustrated on pi. vi and other plates at the end of the volume. The 

 book needs only to be known in order to be appreciated and widely 

 circulated. We commend it to all students of the Mollusca; those 

 who are not will bv reading it no doubt become so. 



II. — British Pisidia. 

 Catalogue of the British Species of Pisidium (Recent and Fossil) 

 in the Collections of the British 'Museum (Natural History), with 

 notes on those of Western Europe. By B. B. Woodward, F.L.S., 

 etc. 8vo ; pp. x, 144, with 30 jjlates. Loudon : printed by 

 order of the Trustees of tlie British Museum, 1913. Dulau & Co., 

 Ltd., 37 Solio Square, W. Price 10s. &d. 



OF all the groups of British freshwater shells the Pisidia have 

 hitherto been the most puzzling. JS^o two authorities have 

 been in agreement and no real test for the species had been noted. 

 It must therefore be a great relief to students to find that at last 

 the golden key has been discovered by B. B. Woodward, who in this 

 monograph shows clearly that the various species can be correctly 

 differentiated by their hinge structures. 



Pioneer work of this character is not easy. First it had to be 

 shown that hinge characters were constant ; then the various species 

 had to be discriminated and identitied with forms previously described 

 on shell form alone; and lastly the whole of the available material 

 had to be examined and compared. The result of all this labour is 

 the volume before us, a volume which will be the foundation of all 

 future work, and everyone who has hitherto vainly tried to identify 

 Pisidia is now under a deep debt of gratitude to Mr. Woodward. 

 AVhen we mention that nearly one hundred described species are 

 sunk as synonyms the literary labour alone of the author can be 

 appreciated. Seventeen species are dealt with ; fifteen of these are 

 British, one is a living Continental, and one an extinct Pleistocene 

 Belgian form. It is noteworthy how the species have existed 

 unchanged in the British Islands for a very long period. One form 

 ranges from the Coralline Crag (Pliocene) of Suffolk to the present 

 day ; four living species are known from Norwich Crag (Pliocene) 

 times, and five recent species make their first appearance in the 

 Cromerian (Forest Bed) of West Runton, Norfolk, whilst one species 

 ranges from the Norwich Crag to the Pleistocene of Crayford. 



Environment plays a considerable part in the variation of shell 

 form, and the differences between river forms and lake forms are 

 fully dealt with. Non-recognition of this non-significant variation 

 has in the past been the cause of the multiplication of species. 



An excellent feature in the volume is the series of typomaps, thus 

 enabling the reader to ascei'tain at a glance the exact range of any 

 species on these Islands. The plates are perhaps a little lacking in 

 clearness of definition, and as the original photos were undoubtedly 

 sharp tliis must be due to the difficulty of printing in numbers. 

 Mr. F. W. Reader deserves praise for his share in this difficult work. 



