104 HOMES WITHOUT HANDS. 



knowii to naturalists, is evident from the shape of the hole and 

 the comparative hardness of the shell and the substances in 

 which it is embedded. The shell is of ordinary hardness, while 

 the rock in which it is found is often of adamantine density. 

 Sometimes it bores into corals, frequently into limestone, and 

 often into shells, which it penetrates as deeply as the date shell. 

 On every rocky shore which the Saxicava inhabits, its burrows 

 may be found, no matter what may be the hardness or composition 

 of the stone. The clay ironstone which is found about Harwich, 

 and is popularly called cement-stone, is filled with the burrows 

 of the Saxicava. Its tunnels are found in the Kentish rag, 

 while even the well-known Portland stone, of which the Ply- 

 mouth breakwater is constructed, is often honeycombed by 

 the multitudes of these bivalves that inhabit it. Some of the 

 enormous stones which were employed in building the break- 

 water are now much wasted by the holes made in them by the 

 Saxicava. 



As is the case with the burrows of the date shell, those of the 

 Saxicava do not run parallel with each other, but are driven into 

 the stone at any angle. In consequence of this custom, it is not 

 of unfrequent occurrence that one of the creatures hits upon the 

 burrow of another, and if it does so, it will not, and in fact 

 cannot, alter the direction of its tunnel. Neither is it able to 

 wait until the other shell has burrowed further, but eats its way 

 silently and unrelentingly along, cutting through the shell and 

 body of its luckless companion, and thus bringing on it a violent 

 death, which its rocky home seems especially intended to avert. 

 The hole is on the average about five or six inches in depth, and 

 the animal does not lie free in its burrow, but attaches itself to 

 the side by means of a byssus or cable, like that of the mussel, 

 save that it is smaller, because the strain upon it is not so great 

 as when the shell is anchored in the open sea. This shell has a 

 very wide range of locality, and is sometimes found at a very 

 great depth, specimens having been procured at a depth of nearly 

 900 feet. It attains its largest dimensions in the colder seas. 



Another member of this family [Xylophaga dorsalis), burrows, 

 as its name implies, into wood and not into stone. It is a small 

 species, and of a very globular form, and never burrows to any 

 great depth, an inch being the ordinary length of its tunnel. 

 The shells of this creature are often found in floating wood, or in 



