Mollusks. 253 



Having thus glanced at some of the reptiles of foreign countries, 

 we may proceed to such as are indigenous in these islands, and to 

 which, more properly, Mr. Bell's volume is appropriated. 



Robert Patterson. 



3, College Square North, Belfast. 



(To be coutiuued) 



Note on the rapid increase of the Polymorphous Muscle (Dreissena 

 polymorpha) in Great Britain. By Robt. John Bell, Esq. 



It may not, perhaps, be altogether uninteresting to some of your 

 readers, to have pointed out to them a few fresh localities for this 

 beautiful mollusc, which is now becoming generally diffused over the 

 rivers and canals of England. The precise time of its introduction 

 will probably never be correctly ascertained, although its appearance 

 in one place, as a centre from which radii diverge in different direc- 

 tions, may in some degree tend to elucidate its history. Many habi- 

 tats for this species are mentioned by H. E. Strickland, Esq., in a 

 paper published in the second volume of Charles worth's continuation 

 of Loudon's * Magazine of Natural History.' The place to which I 

 would particularly direct your attention, is the Port of Goole, in York- 

 shire, belonging to the Aire and Calder Company, where are several 

 large docks for the reception of shipping, and which, I believe, were 

 opened either in 1828 or 1829. In three or four years after this, I 

 was greatly surprised, on seeing the water drawn off a few feet lower 

 than usual, to find the walls of the docks completely covered with this 

 shell ; and 1 do not at all exaggerate when I say, that without much 

 difficulty, pecks might readily have been procured. Here they are to 

 be seen attached by their byssus, not only to the walls, but to stones, 

 fragments of wood, the live shells of Anodon Cygneus, and the dead 

 ones of their own species ; and ii'om the numbers of the latter now 

 to be found, it is quite evident that many generations have passed 

 away. One dock is entirely appropriated to the bonding of foreign 

 timber, which frequently remains some months prior to its being re- 

 shipped, or floated on rafts down the rivers or canals to the various 

 inland towns ; during which time, those pieces which adjoin the sides 

 or touch the bottom are sure to be covered over by this shell. Hence 

 it naturally follows that its distribution over the West Riding of York- 

 shire, and the adjacent counties which have any communication with 

 the canals of the Aire and Calder Company, will fail to excite sur- 



