where its transport has doubtless been effected by means of timber. I only know of one instance to the contrary, which is that of the Leam, at Leamington, where it has been found of a large size by Dr. Lloyd of that place. But though the Leam itself is not navigable, yet it is in the immediate vicinity of the canal, from which the Dreissena has probably been introduced. I have further to add that this shell has lately been planted by Mr. Stuchbury of Bristol, in some of the waters near that place.
"It appears desirable to record these particulars, because it may interest some of our field-naturalists to watch the gradual spread of this species over the kingdom. Its propagation is so astonishingly rapid, that it will probably become, in a few years, one of our commonest British shells.
"I lately kept some of these molluscs, of different ages, alive for some time in a basin of water. The full-grown individuals, though they had been torn from their native bed, soon secreted a fresh byssus, and became anchored to the bottom of the basin. It is evident from this, that the byssus, when first secreted, must be in a highly glutinous state, which enables it to become attached to the smooth surface of glazed earthenware. The young individuals still retained the power of locomotion, and crawled like gasteropods over the bottom. They effected this by protruding their foot in advance of the anterior or cardinal end of the shell, and advanced by alternate expansion and contraction of this foot, dragging the shell after them. They indulged their wandering propensities for a few weeks, and then wisely followed the example of their parents, by selecting some convenient nook, to which they attached themselves contentedly for life.
" I further remarked that these molluscs, acephalous though they be, have still an evident perception of light. When in a quiescent state, they kept the shell partly open, with the siphuncular and branchial apertures exposed; but if any object was suddenly brought over them, they immediately receded, and partially closed their valves, although care was taken that no concussion should be given to the basin.—Mag. Nat. Hist. New Series, ii. 362.— 1838.Note on the multiplication of Dreissena polymorpha. Those of your readers who study the geographical distribution of animals, may feel interested to know that the small bivalve shell, Dreissena polymorpha, has found its way to various canals and other waters in Leicestershire; and a few days ago, I discovered it in immense numbers in the Grand Trunk Canal, at Burton, adhering to the stones that form the embankments, and to the shells of Anodons and Unios. It is in the latter situation, deep in the mud of the canal, that I find by far the largest specimens; several of these measured more than an inch and a half in length. If this species go on increasing in the same ratio as it must have done, supposing it to have been introduced into Britain only about twenty-five or thirty years,—our canal will shortly become literally paved and lined with its shells.—Edwin Brown; Burton-on-Trent, June 29, 1843.
Note on Shells and Crabs at Circular Head, Van Diemen's Land. "Shells are also numerous here, we picked up more than a hundred species. The sand north of the bluff, was sometimes covered with myriads of globular crabs, about the size of a hazel-nut. On going among them, they made a noise like a shower of rain, and by a rotatory motion, in a few seconds, buried themselves in the sand, the surface of which they left covered with pellicles like peas."—J. Backhouse's 'Narrative of a Visit to the Australian Colonies,' p. 108.
