2l6 THE DISPERSAL OF SHELLS. 



time, also, it was observed in Scotland, where, as men- 

 tioned by Dr. J. Scouler of Glasgow in 1833, it was 

 found living in vast abundance towards the eastern 

 extremity of the Clyde and Forth Canal ; and, in the 

 following year, its discovery in the Union Canal, near 

 Edinburgh, was communicated to the Wernerian Society 

 by Mr. Stark.^ In 1836, the Rev. M. J. Berkeley found 

 the species in plenty on the piers of a bridge crossing 

 the Nen at Fotheringhay, Northamptonshire, and also, 

 a little higher up the same river, on the stones of a 

 small overfall at Tansor. He had formerly examined 

 the stream carefully, for several successive years, both 

 above and below these spots, without detecting the 

 creature, and had reason to believe that its establish- 

 ment was of recent date (subsequent to 1828) ; pro- 

 bably, he thought, it had been introduced from Wis- 

 beach on timber."^ As to the date of its detection at 

 the last mentioned place I know nothing. In 1837, 

 Mr. Strickland discovered it in the Avon, near Evesham, 

 in Worcestershire. From 1828 to 1834 he was in the 

 habit of conchologizing frequently in that river, and 

 could scarcely have failed to detect the creature if it had 

 then lived there, but none occurred. In 1837, however, 

 after an absence from England of two years, he was 

 greatly surprised on finding several of its shells among 



' J. Scouler, Loudon's "Mag. Nat. Hist.," vi. (1833), p. 532 ; 

 Stark, as quoted by Berkeley, Loudon's "Mag. Nat. Hist.," ix. 

 (1836), p. 572. 



' M. J. Berkeley, Loudon's " Mag. Nat. Hist.," ix. (1836), 

 PP- 572-3. 



