DISPERSAL BY MAN. 21/ 



refuse on the banks of the river, and on further search 

 he found that the animal had become completely estab- 

 lished on the gravel of the river-bed ; several hundred full- 

 grown specimens were collected in the course of an 

 hour; "there is, therefore, clear evidence of the recent 

 introduction of this mollusc into the Avon, and of the 

 rapidity with which it has reached maturity and multi- 

 plied." In the same or the following year, Mr. 

 Strickland observed the species in the canal between 

 Warwick and Birmingham, and, in a paper dated in 

 1838, he stated that it had been found also in the 

 canals near Wednesbury, in Staffordshire, and in the 

 Learn at Leamington ; the latter water is not navigable, 

 but is near a canal from which the Dreissena was pro- 

 bably introduced. In the same paper Mr. Strickland 

 stated that the animal had been " planted " in some of 

 the waters near Bristol.* About 1838, also, it was 

 detected in the Lesser Nen, which runs through the 

 town of March,- and about the same time a specimen 

 was obtained in Nottinghamshire from unnavigable 

 water — an old mill-dam at Toton, supplied by the 

 Erewash, a small shallow stream joining the River 

 Trent nearly a mile from the place — that river being 

 the nearest navigable water ; afterwards (before 1846) 

 numbers were found "adhering to stones underneath 

 the water-fall of a pond at Lenton " in the same county, 

 to which they must have gone up a very small brook 



* H. E. Strickland, Charlesworth's "Mag. Nat. Hist.," (n.s.), i. 

 (1838), pp. 361-3. 

 ^ S. Smith, "Science Gossip," for 1868, p. 238. 



