io6 



THE BRITISH NATURALIST. 



entirely uninjured, exhihiting slight modifications of the characteristic 

 deformities described above,^ and the constant repetiton of accident 

 renders the hkehhood that its results will be persistently reproduced, 

 much more probable than in the accidental cases of deformity which 

 we observe under ordinary circumstances.'' The Rev. S. Spencer 

 Pearce has written a paper on H. caperata, of Avhich I shall give an 

 abstract. The author remarks that we have to deal with " Variations 

 of Size, of Markings or Colouring, of Form or Shape.'" . . " With 

 regare to the variations in size, we have as the extreme of largeness the 

 var. wiiij^r, while the extreme towards smallness . . . would have 

 to be characterised as a var. minor.'' "Judging from the fact that the 

 larger forms of Helix caperata, as also those of Helix virgata are 

 found on arable ground, especially in the borders of cultivated fields 

 in limestone districts, size would seem to depend only on the 

 combined presence both of an abundance of food-plants such as are 

 supplied in the cultivated field, with a calcareous soil. Proper 

 herbage, apart from the calcareous earth, and vice-versa, the calcareous 

 soil without the richer food-plants, will not suffice to increase the 

 shells in size." The writer omits any reference to climate which j 

 think should always be considered a factor, a suitably warm tempera- 

 ture aided by a free supply of moisture would, I believe, be found 

 necessary for the developement of tiiese shells to any extent beyond 

 the usual size. As the writer however is dealing with the County of 

 Sussex, the presence of these climatic conditions are not doubtful. 

 The author next states his opinion as to the origin of the two varieties 

 of form which he has observed, the one a compact form with a raised 

 spire and banded, the other, a mottled form, with a flattened spire 

 and a T\nd^ umbilicus (var. gigaxii]. The writer states that the latter 

 is found in the borders of fields, while the former keeps entirely to 

 open downs and pastures, and uncultivated places. The reason of 

 this IS believed to be that in tilled fields the flatter shell is of more 

 use, enabling the snail to crawl with house low down close under the 

 matted leaves, where it leads a sluggish life, rarely, if ever seeking to 

 climb. On the turf and grass, on the contrary, a more compact, 

 smaller and_ handier shell is required that the animal may the more 

 easily manoeuvre up and down, in and out among the blades of grass. 

 The v\'riter remarks that the flattened and mottled form is almost 

 universal in those localities where sheep never feed, the banded form 

 (var. ornata) occurring very rarely, while on the sheep pastures 

 (commons, &c.) he finds ornata almost equally abunbant with the other 

 form ; this he accounts for by supposing that the sheep find the snails 

 an unpleasant addition to their ordinary food, and further that the 

 more conspicuous banded shells are easily avoided, while the less 



* The Italics are mine. 



