Land and Freshwater Mollusks. 43 



England : of fifty specimens which I collected in the Isle of Port- 

 land, about six distinct groups may be made. In this shell, 

 ordinarily much coloured with various shades of brown, an in- 

 teresting variety occurs, which as yet I have only found in one 

 locality ; the ])osition of the bands is marked, but they are colour- 

 less, and show as semi-transparent lines on the opaque white 

 whorls ; the effect is curious, and seems to arise from the same 

 want of power to secrete colouring matter, alluded to above in 

 other species. I have observed lately, near St. Denis, numbers of 

 this Helix, but all of one variety, common also in England, almost 

 wholly opaque white, without the transparent bands just mentioned. 



The most attractive in colour of British land shells are those 

 of Helix hortensis and nemoralis already alluded to; these are the 

 bright yellow and dark striped species frequent in hedges and 

 water sides : their varieties are numerous, upwards of ninety have 

 been distinguished by a French writer, Moquin-Tandou, for these 

 snails are especially abundant in France, and are largely supplied 

 to the markets, so that he has had opportunities of examining 

 baskets containing upwards of one thousand each. The naturalist's 

 object in this search after varieties is not mere curiosity, some law 

 which controls them may yet be discoverable ; the collector 

 indeed is stimulated by the rarity of some, for example, you can 

 make a series of Helix nemoralis, beginning with a yellow specimen 

 unstriped and continue with specimens having one, two, three, 

 four, and five bands — the bauds are to be fully seen on the lower 

 whorl — but you may examine two thousand specimens before you 

 find a well marked example with six stripes : why is this and how 

 is this ? is it development, perfection, or deterioration ? the search 

 for answers to such queries prevents the collector's work from 

 degenerating into laborious trifling. 



I would gladly touch on the effects of food and some peculiar 

 conditions of life, on these little animals and their habitations, 

 but must pass on to other points — one remark I may make about 

 the fresh water species — where lime is abundant in the water the 

 shells are not always large, as might be expected, but are rather 

 compact, thick, somewhat rugged and strong, the abundance of 

 food for the animal and the quality of the food determines the 

 expansion of the shell, and thus in still ponds full of vegetable 

 growth, where conditions of temperature are favourable, some species 

 attain unusual size. The water-weed anacharis now too abundant 

 is, I find, a food which stimulates the growth of some of the 

 Limnaji: the more they eat of it the better. 



Allusion has been made to the possibility of discovering the laws 

 which have determined the distribution of these land and freshwater 

 inoUusks : to make discovery of the laws of the distribution of 



