MASEFIELD : THE ECONOMIC USE OF SOME BRITISH MOLLUSCA. 1 55 



acicula. And then we have the freshwater mollusca, thus showing that 

 these animals are to be found really everywhere. 



The habitations of man appear to have a special attraction for many 

 species, no doubt on account of the surrounding cultivation affording 

 tempting food, and the crevices of man's buildings providing safe 

 retreats during the day. On the other hand, non-cultivation appears 

 to be necessary to the survival of some species. Gwyn Jeffreys says on 

 this subject : — " There is probably not a square rood of land either 

 in a cultivated or uncultivated state, or covered with fresh, brackish, 

 or salt water, that is not inhabited by mollusca of various kinds. 

 Trees and herbage are the chosen stations of many sorts, for the sake 

 of the shelter or food which they afford ; and even our cellars and 

 kitchens are not free from them." Again, Mr. Lionel E. Adams, in 

 his excellent " Manual " says of Agriolimax agrestis that it " swarms 

 everywhere," of Helix rotundata "found everywhere in sheltered 

 spots," and of Limncea peregra " distributed over every part of the 

 Eastern Hemisphere." The truth of these statements I am now able 

 to confirm as far as this country is concerned. A correspondent in 

 Herefordshire, on a plot of cultivated land, 95 yards long by 5 yards 

 wide, and therefore containing 475 square yards, placed 100 flat 

 pieces or boards of old decaying wood, each about 18 inches long by 

 6 inches wide, and during three consecutive years the average number 

 of snails and slugs taken from under these boards was 18,000 per 

 annum, but it must be borne in mind that at least a quarter as many 

 more would be taken by thrushes and other birds on the same ground. 

 Each of these boards, my informant states, at first produced about 

 sixteen molluscs every three days. The annual average has now be- 

 come reduced to only 300 molluscs, and this year only 152 have been 

 taken on the same ground, showing that it is possible by these means 

 to almost exterminate these animals altogether in a given area of 

 ground within a given time. On another patch of ground, containing 

 only five square yards, two similar boards to those I have described 

 were placed, and these yielded on a first examination 44 slugs, next 

 time 22, then n 3 and afterwards only 1. These slugs and snails are 

 stated to have comprised 13 species, but now only 6 species are to be 

 found on the same ground, the others, it is presumed, have become 

 exterminated. As to the exact species, I am sorry to say that I have 

 not sufficient evidence at present to identify them. Similar experi- 

 ments made by myself in my own grounds give an average of 15 to 

 20 slugs (principally Agriolimax agrestis and Arion hortensis) to be 

 found on every square yard of ground, and I believe about the same 

 average will be found generally over all pasture, arable, and other 

 land ; this may easily be ascertained just at dusk any wet or damp 

 evening during open weather with the aid of a lantern. 



