On the Mollusca of the Club District. 145 



of which no less than forty-one have been named by various 

 authors as inhabiting Europe. This dreadful array has now been 

 brought down to six species, of which five inhabit Great 

 Britain. In Surrey we have all these, and they may all be 

 found, some in the rapid little streams, and some in the ditches 

 and swamps in the low lying ground between Merstham and 

 Bletchingly. The variet}- obtusalis of P. pusilhim occurs in 

 ditches at Charlwood. The only safe plan to adopt with this 

 genus is to collect specimens from numerous localities and to 

 compare them, and more important still to compare them with 

 good collections. 



Of the larger mussels, the C7«io5and^7?0(/o«5, we have plenty. 

 Anodon cygneus of a very large size occurs on Fetcham 

 Common, A. anatina in the stream west of Nutfield Marsh, 

 Unio pictonun in the river Wey near Guildford, and Unio 

 tjwndus in the Basingstoke Canal. The stomachs of these 

 bivalves yield many kinds of diatoms. Unio uiargaritifer, the 

 true pearl mussel, seems to be entirely a northern type. I 

 made the attempt though unsuccessfully to introduce it here 

 seven years ago. One hundred and fifty Unios were forwarded 

 from the river Don in Aberdeenshire, and deposited July, 1875, 

 in what appeared suitable localities in the Wandle, between 

 Bridge House, Wallington, and Hackbridge. The weather, 

 unfortunately, became very hot at the time of transit, and the 

 mussels, which were packed in wet moss, were rather languid 

 when put in the river. The sickly ones were immediately 

 attacked by the leeches ; fifty-two mussels were taken out dead 

 within a week. None appear to have survived long. It is 

 worthy of note that the waters of the river Don, in its lower 

 part where the pearl mussel lives, contain only 5-8 grains 

 inorganic matter per gallon, whereas the Wandle holds in 

 solution upwards of 19 grains inorganic matter per gallon. 

 The Don which contains so small a quantity of lime, produces 

 a shell which is remarkably thick and strong; the Wandle, con- 

 taining three times as much lime, produces shells which are 

 thin and fragile. On the other hand the Don has 2*5 grains 

 organic (that is vegetable) matter per gallon, and the Wandle 

 only 174 grains. Dreissena polymorpha occurs in great plenty 

 in the stony shallows at the junction of the Rivers Wey and 

 Thames, but these specimens are totally devoid of markings. 



Gasteropoda, or water breathing snails. — Neritina fluviatilis, 

 themost singular in appearance of all our shells maybe taken in 

 the Thames at Weybridge, in places where the bed of the 

 river is shingly. The snail will not live in captivity. Pahidina 

 vivipara is widely spread over the western district in the Wey, 

 the Surrey and Sussex Canals, and the Basingstoke Canal, 

 those from the latter place being of a lighter colour. My friend 



