Page:The Zoologist, 1st series, vol 1 (1843).djvu/282

254 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 extends 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 Scarborough, 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 unfrequent. Should this slight sketch prove of any advantage to naturalists, 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 habitat, 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.

[The following are extracts from Mr. Strickland's paper referred to above. See also Mag. Nat. Hist. 572 and 643.— Ed.]

"From the year 1828 to 1834 inclusive, I was frequently in the habit of conchologising 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 slightest 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 completely 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 Wednesbury in Staffordshire.

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