94 THE DISPERSAL OF SHELLS 



wich Islands, wonderfully isolated in mid-ocean, are 

 inhabited, as we have just seen, by three or four hundred 

 land species, and possess only "a few fresh-water 

 shells."^ It seems evident enough from facts of this 

 kind that effectual means for occasional transportal 

 are certainly possessed by land-molluscs, and even in 

 local distribution within a given country we see much 

 which in the absence of means for dispersal, at least 

 over land, would seem well-nigh inexplicable, for more 

 or less isolated colonies of certain species are not un- 

 frequently found at great distances from others of their 

 kind. Mr. Standen adverted to this subject in a com- 

 munication with which I was favoured in 189 1, remarking 

 that he had often pondered over the question as to 

 "how and when certain colonies of land-shells had 

 become located in various queer places,'^ and referring, 

 for instance, to two singular colonies of Vertigo pygmcea 

 in which the creatures live in great abundance within 

 limited areas, and to the presence of the heath-snail, 

 Helix ericetormn, on a little bit of rough land in the 

 middle of a cultivated field, many miles from any other 

 habitat of the species. In Norfolk, according to 



ton, " Testacea Atlantica," 1878, p. 6; more recently the total 

 number of land-shells truly indigenous to St. Helena has been 

 estimated by Mr. Edgar Smith as twenty-seven, of which, it is 

 said, seven only are now living on the island, the remainder 

 having been exterminated by the destruction of the forests : see 

 report of the Zoological Society's meeting on 5th April, 1892, in 

 "Nature," xlv. (1892), p. 597. 



^ " Island Life," pp. 293, 298, and 303 ; ed. 2, pp. 305, 310, and 

 316. 



