224 1'HE DISPERSAL OF SHELLS. 



also, that the two colonies near that city were distinct 

 and separate introductions. The presence of the crea. 

 ture, in thousands, in a cistern on the top of an engine- 

 house at Burnley, " about sixty feet above the canal,'^ 

 has already been referred to. The shells had been 

 pumped from the canal, no doubt, with the water 

 supplying the cistern. As suggested by Mr. J. R. 

 Wildman, the creature was probably carried by birds to 

 the ''paper-works lodge." 



These are the only places in Britain, as far as I am 

 aware, in which P. dilatatus has been detected. It is 

 now nearly a quarter of a century since the first 

 specimens were found, and it is surprising that the 

 creature has not, by this time, extended its range beyond 

 the limits of Lancashire, the county to which it was 

 imported ; within that county, as we have seen, it has 

 been found in four separate localities.^ 



Physa acuta Drap. In the spring of i860, speci- 

 mens of this pond-snail were found by Mr. A. Choules 

 in a water-tank in the Royal Gardens at Kew, whither 

 they are supposed to have been imported from abroad 

 with aquatic plants." The shells, it is said, were un- 



' J. G. Jeffreys, '' Ann. and Mag. Nat. Hist.," (4), iv., (1S69), pp. 

 341-2; T. Rogers, " Science Gossip" for 1870, p. 138; "Quart. 

 Journ. Conch.," i. (1875), P- ^i ; " Conchologists' Exchange," i. 

 (1887), p. 63; "Journ. of Conch.," v. (1887), pp. 218-220; R. Rim- 

 mer, " Land and Fresh-water Shells," 1880, pp. 47-9 ; E. Collier, 

 "Journ. of Conch.," iv. (18S4), p. 217 ; J. Bates," Journ. of Conch.," 

 V. (1887), P- 221 ; J. R. Wildman, " Science Gossip," xxiv. (1888), 

 p. 210 ; F. C. Long, " Science Gossip," xxiv. (1888), p. 281. 



^ It is doubtful whether P. acuta was previously known in 



