122 HOMES WITHOUT HANDS. 



shells, which is remarkable for the depth to which it -bores, and 

 the hard nature of the substances through which it makes its way. 

 This is the shell called Saxicava rugosa; one of the most variable 

 of the moUusks, so variable indeed that no less than fifteen differ- 

 ent names have been given to it, each being supposed to be a 

 separate species. Not only species, but even genera have been 

 formed from the varieties of this curious shell. It is a flattish bi- 

 valve, of no very great size, symmetrical in shape when young, 

 but oblong when old. 



This creature burrows as rapidly as the species which has just 

 been described, and the process by which the feat is accomplished 

 is quite as enigmatical. Several conchologists have expressed an 

 opinion that the animal must secrete some liquid solvent, which 

 softens the rock, and permits the shell to pass. But, although it 

 is possible for the boring snail to' excavate by such means, the 

 Saxicava can hardly do so. For the boring snail is a terrestrial 

 species, and would be able to employ a solvent without interrup- 

 tion ; but as the Saxicava works below the surface of the sea, any 

 solvent which it could employ would be either washed away, or 

 so diluted by the water that it would have no effect upon the 

 stone. 



Still, that the creature must employ some means not yet known 

 to naturalists is evident from the shape -of the hole, and the com- 

 parative hardness of the shell and the substances in which it is 

 imbedded. 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 iron-stone which is found about Harwich, and is popu- 

 larly called cement-stone, is filled with the burrows of the Saxi- 

 cava. Its tunnels are found in the Kentish rag, while even the 

 well-known Portland stone, of which the Plymouth breakwater 

 is constructed, is often honey-combed by the multitudes of these 

 bivalves that inhabit it. Some of the enormflus stones which 

 were employed in building the breakwater 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 



