66 JOURNAL OF CONCHOLOGY. 



ON THE 



EROSION OF CERTAIN FRESHWATER SHELLS. 



By GEO, W. SHRUBSOLE, M.C.S. 



[Read before the Conchological Society, June 3rd, 1886.] 



In October, 1884, I gathered from the Trent Canal at Stone, 



Staffordshire, twenty specimens oiPlanorbis corneus. They were 



all young, the larger ones hatched probably the previous year, and 



the smaller the preceding spring. My reason for selecting them 



from this locality was that, so far as I know, they do not occur 



in Cheshire, and this was the nearest habitat. My object was 



experimental- — to watch their growth under certain conditions 



of food, etc. For this purpose I selected a glass jar capable of 



holding one gallon of water, and so placed as to be continually 



under my observation. Various water plants were added, to 



supply food and aerate the water. Either the altered conditions 



of their existence were unfavourable, or the food unsuited ; 



certain it is that they led a very inactive life at first. Winter 



was soon at hand, and they became more inactive than before. 



The introduction of water-cress as a food, coupled with the 



return of spring, brought new life and activity. From this 



period, the spring of last year, the supply of food in the shape 



of water-cress — and when that failed, lettuce — -was very liberal, 



as may be inferred from the fact that during the months of June 



and July the amount of food consumed weekly was over four 



ounces in weight. A record was kept of the food supplied and 



the growth made during the time. After they had been under 



my observation three or four months, a result presented itself 



which I had not originally contemplated, and which I now wish 



to bring before the members of the Conchological Society. 



The shells of the Planorbes, when I gathered them, were 

 intact and well developed. After some time I noticed that, 



J.C., v., July, 1836. 



