The Mo/hiwa of Cambridgeshire 



Unio pictorum and U. twnidus. Mrs Hughes informs me 

 of the occurrence of these species at Barrington. Their dis- 

 tribution is probably local in the county. 



Sphaerium corneum. In June 1901 Mr A. E. Shipley 

 found that a choking of the inflow of the Bathing Pool in 

 Christ's College Garden was caused by clustered masses of 

 this form. Jenyns 1 mentioned "a small globular variety" as 

 common in the Fens. 



The Pisidia are well represented in Cambridgeshire, and as 

 long ago as 1832 were with Sphaerium the subject of a mono- 

 graph by the Rev-. L. Jenyns 2 . His nomenclature was revised 

 by Jeffreys 3 , but our knowledge of the line between species and 

 variety in Pisidium is still unsatisfactory. The writer has here 

 followed the provisional nomenclature of Mr B. B. Woodward 4 . 

 P. amnicum is common and is found more often in moving 

 water than in pools. Jenyns recorded that Prof. Henslow 

 found several varieties in the neighbourhood of Cambridge. 

 The P. obtusale of PfeirTer, either a distinct species or a 

 variety of P. pmillum, was found by Jenyns chiefly in 

 stagnant waters and often in the same spots as the Physidae. 

 P. nitidum occurs in clear waters, while a common form is 

 the P. pulchellum of Jenyns. P. henslowianum, Jenyns, was 

 first found by Prof. Henslow in ditches joining the Cam at 

 and below Cambridge. P. amnicum and P. puxilhnn have 

 also been found in the north of the county. 



Pleistocene Species. 



We may now turn to the occurrence of mollusca in the. 

 post-tertiary deposits of the district. In addition to the 

 forms they contain which are also living at the present time 

 the Pleistocene beds yield a number of species which are now 



1 "British Species of Cyclas and Pisidium," Tranx. CuinJi. I'liil. S<><-.. 

 1832, p. 289. 



2 loc. cit. siifini. 3 loc. tit., pp. 1028. 



4 "List of British Non-Marine Mollusca," Journ. C<ich., x., 1003, 

 p. 353. 



