21 8 THE DISPERSAL OF SHELLS. 



fully a mile from a canal, where, however, though the 

 observer had frequently searched, he had never found 

 them.^ The animal was known to occur in streams 

 near Exmouth, in 1842. By 1843 it is said to have 

 found its way to various canals and other waters in 

 Leicestershire, and it had been discovered in immense 

 numbers in the Grand Trunk Canal at Burton, Stafford- 

 shire.- Captain Brown^ in 1844, stated that it was 

 common in the Bridgwater Canal, and also " in many 

 places in the canal betwixt Manchester and Hull," and 

 in that year it was noticed, also, on timber in the Ouse, 

 near St. Neots, Huntingdonshire.^ We find, therefore, 

 that within twenty years from the announcement of its 

 discovery D. polyviorpha was known in two localities in 

 Scotland, and in England in the counties of Surrey, 

 York, Northampton, Worcester, Warwick, Stafford, 

 Cambridge, Nottingham, Devon, Leicester, Somerset, 

 Huntingdon, and perhaps also in Lancashire, and it is 

 of course probable that its range at that time may have 

 been much wider, for I have not made a thorough 

 search for records ; indeed, if a statement by Brown 

 (1844) is to be relied upon, it was then to be ^' met with 

 in most of our canals." It would be interesting to 

 ascertain the creature's range at the present time, 

 but to find, and search, all the local lists and notes 



* G. Wolley, "Zoologist," iv. (1846), p. 1420. 



' L. M. Pratten, " Science Gossip," for 1868, p. 189 ; E. Brown, 

 *' Zoologist," i. (1843), P- 255. 



^ T. Brown, ''Illustrations," ed. 2, (1844), p. 76; C. Prentice, 

 "Zoologist," V. (1847), p. 1651. 



