254 



Mollusks 



prise. It is very tenacious of life, and exceedingly prolific, provided 

 the locality be favourable. 1 found it attached to stones &c. in the 

 river Don, at Conisbro' near Doncaster, in 1836, along with many 

 dead shells, clearly proving that it had been there some time ; also in 

 the Barnsley canal. 



It is worthy of remark, that as far as the influence of salt water ex- 

 tends into the dock, when the gates are opened into the Ouse for the 

 ingress or egress of vessels, not one solitary individual can be found, 

 the line of demarcation being as perfect as the joint between one 

 stone and another in a wall. My friend Wm. Bean, Esq., of Scarbo- 

 rough, planted it near that place a few years ago ; but in a recent 

 communication he states he thinks they have all perished. 



In no instance have I been able to discover the crystals mentioned 

 by Mr. Sowerby (Mag. Nat. Hist. ix. 643), though I have examined 

 hundreds of specimens ; pearly concretions, however, are not unfre- 

 quent. Should this slight sketch prove of any advantage to natural- 

 ists, by throwing a little light on the history of this mollusc, the object 

 of the writer will be fully answered ; who, having resided many years 

 in the neighbourhood, and watched the subject with attention, simply 

 records the facts as they have fallen under his observation. 



It is highly probable that in the first instance this mollusc came 

 attached to timber from the Baltic, and having found a congenial ha- 

 bitat, has multiplied in this extraordinary degree ; its tenacity of life 

 being fully capable of sustaining it during the voyage, in the damp 

 hold of a ship. Robert John Bell. 



Mickleover House, near Deity, 

 June 5, 1843. 



[The following are extracts from Mr. Strickland's paper referred to above. See 

 also Mag. Nat. Hist. 572 and 643.— Er^.] 



" From tlie year 1828 to 1834 inclusive, I was frequently in the habit of concholo- 

 gising in the Avon, near Evesham, during which period, if the Dreissena polymorpha 

 had inhabited that river, I could scarcely have failed in detecting it. Not the slight- 

 est vestige of it however occurred to me during that time. An interval of two years 

 elapsed, in which I was absent from England ; and in the beginning of 1837, I was 

 much surprised at finding several specimens of this shell among the refuse on the 

 banks of the river. On further search I found that the Dreissena had become com- 

 pletely established on the beds of gravel in the river; and in the course of an hour I 

 collected several hundred full-grown specimens. 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 multiplied. 



"I have since observed it in the canal between Warwick and Birmingham, and it 

 has also been found in the canals near Wedncsbury in Staffordshire. 



" In all the cases hitherto cited, this shell has been found in navigable waters, 



