Indurated mud, clay, and wood are perforated by these animals as well as stone, and their boring habits render them objects of painful anxiety to those who are interested in submarine works. The ship-worm (Teredo), whose terrible ravages have been already alluded to (see ante, p.' 41), is a member of this family, though the great elongation of its body, the minuteness of its valves, and the shelly tube with which it lines its burrow, long caused it to be associated with the Worms (Annelida), rather than with the Mollusca.
The fullest and most carefully prepared account of the natural history of this animal was communicated by Mr. W. Thompson to the Edinburgh New Philosophical Journal, from which paper the following interesting details of one of our British species (of which we have unfortunately no fewer than six) are extracted: —"The greatest diameter of the testaceous tube or case, at the larger end, is seven-eighths of an inch; at the smaller, it varies from one and a half to two lines. All of the specimens have from one and a half to two inches and upwards of the smaller end of the tube greatly contracted within by laminæ, also the partition producing the double aperture extending but a few lines from the very extremity. The greatest thickness of the shell is at the smaller end, where, at the commencement of the laminæ, its consistence is from one-twentieth to one-fortieth part of an inch: from this it becomes gradually thinner towards the greater end, which in the very largest specimens is found to be closed up, but in several others there is no deposition whatever of testaceous matter for some distance from the termination of the cell. In one perfora-