22 THE DISPERSAL OF SHELLS. 



last mentioned, and certainly there is no such possibility 

 in a further case which Mr. C. P. Gloyne has obligingly 

 communicated. In Jamaica (where Mr. Gloyne resided 

 for some years) is a district in which — owing to the rain 

 percolating through the porous limestone and escaping 

 subterraneously — there is no natural standing or running 

 water; a supply is obtained, however, from artificial 

 cemented-tanks, which receive the rain-water from the 

 "barbecues" (sloping planes, also cemented, for drying 

 coffee, &c.) and from the houses, and in all these tanks, 

 having, as I am assured, no connection whatever with 

 each other, one and the same species of Physa, of which 

 Mr. Gloyne forgets the name, makes its appearance ! 

 Hardly less remarkable, perhaps, is the presence of 

 pond-snails in the basins of both the fountains in Tra- 

 falgar Square, erected in 1845, ^.nd supplied from two 

 Artesian ivells, one behind the National Gallery, and 

 the other immediately in front of it.^ Within nine or 

 ten years after their construction, the basins were known 

 to contain shells, for, about the year 1854, Mr. E. L. 

 Layard exhibited specimens of them at a meeting of 

 the Zoological Society, and, notwithstanding the fact 

 that the basins are said to be frequently cleaned out, 

 I found Lhnncea peregra still living there, in 189 1, in 

 good numbers. A very small fish and a water-beetle, 

 no doubt an Aciliiis, were also seen, but there were no 

 weeds. Artesian wells have been known to send up 

 seeds, small fish, and shells of several kinds, including, 



^ See " Old and New London," (Cassell), ill. 142 ; " Builder," 

 ii. (1844), 370, and iii., (1845), iii. 



