144 ^''- Kenneth McKean. 



rather directed towards encouraging a taste for conchology 

 among the younger members of our newly formed club, and 

 assisting them with advice as to the methods of collecting 

 shells and preparing them for the cabinet, than placing on 

 record a list of the molluscs which live within our boundaries. 



Croydon being situated so close to the edge of the county, I 

 have included in my working ground, in addition to the whole 

 of Surrey, that small portion of Kent which is enclosed by 

 the river Darenth. The botanical sub-committee also adopted 

 that line as their eastern boundary. 



The district throughout offers considerable diversity of soil. 

 In our immediate neighbourhood the chalk is well known to be 

 particularly favourable to many kinds of snails. Near to 

 Croydon we have but little water of that kind which yields a 

 harvest to the conchologist, but the western part of the county 

 is rich in ponds, ditches, and marshes, streams both rapid and 

 sluggish, and certainly not least in importance an almost 

 disused canal. On the eastern side of the district near to the 

 junction of the Thames and the Darenth are brackish ditches, 

 within tide marks, which yield several species found only in 

 those circumstances. I will not detain you by dealing with 

 the arrangement and classification of the mollusca, but will at 

 once proceed to note very briefly the genera that occur in our 

 district, offering a few remarks upon less common species. 



Accepting the system of Gwyn Jeffreys as being the most 

 commonly used at the present time, we commence with the 

 Bivalves. 



Of the genus Sphcerium we have all the species with the 

 exception of S. ovale. S. rivicola, a local and scarce shell 

 throughout the kingdom, I have only found in the Basingstoke 

 canal near to Weybridge, the River Wey, near Newark 

 Abbey, and the Wey and Arun Canal, near Cranleigh. I put 

 some of these shells in a small aquarium, but they were so 

 exceedingly active, incessantly ploughing up the bottom in 

 all directions that the delicate epidermis was in danger of 

 being greatly destroyed, so to save their beauty they were 

 placed in the cabinet. This restlessness may, I think, have 

 been caused by the change from their native gently flowing 

 water to the stagnation of an aquarium, for when freshly taken 

 this bivalve shows little or no signs of abrasion. S. lacustre 

 is widely diffused in Surrey. It occurs in vast numbers on 

 Wandsworth Common as well in the mud as among weeds at 

 the surface. 



The next genus Pisidium requires to be dealt with very 

 cautiously, as two of the species and many of the varieties are 

 difficult to separate. It is comforting to observe that the 

 tendency of modern writers is to reduce the number of species, 



