18 
LITHOPHAGA. 
Boring shells, without accessary pieces or sheath, and 
more or less gaping at the anterior side. Ligament external. 
SAXICAVA. 
GENERIC CHARACTER: Shell bivalve, transverse, the 
sides unequal; gaping interiorly at the superior margin; 
hinge almost without teeth. 
* S. RUGOSA. My til us R. Turt. Lin. Pen. Brit. Zo., 
vol. 4, pi. 63, fig. 72. Mag. Nat. Hist., O. S., vol. 4, 
p. 358. The boring species of shell-fish found in Britain 
belong chiefly t.o the genera Teredo, Pholas and Saxicava , 
for it may be doubted whether any of the other families, 
though found in similar situations, are able to form for 
themselves the chambers they inhabit. The Teredines are 
found only in wood, which when soaked in sea-water they 
readily devour, so that their intestines are found gyeatly 
distended with it, The Pholades prefer the hard rock : 
either the common slate of our coast, which when young 
they readily penetrate, and hollow smoothly out to the 
depth of several inches, with a diameter equal to the com- 
fortable expansion of the shell : or the sandstone found in 
the sea at no great distance. Limestone is also subject to 
their depredations, but it seems, less frequently ; anti when 
the chamber is become sufficiently large for their full 
growth, no further destruction ensues, except from the mul- 
tiplication of individuals. The Saxicava Rugosa, though a 
much smaller Animal, is far more destructive, from being 
much more generally dcstributed, and in greater numbers. 
It lias also of late attracted special attention from having 
spread its ravages along the whole front of the Breakwater 
at Plymouth ; and thereby excited in the minds of some, 
very serious apprehensions for the safety of that edifice* 
Its devastation appears to he confined to substances of 
which a chief constituent is lime ; which it enters when 
young, and which it is never found to penetrate beyond the 
depth of about six inches. It can therefore only bo when 
the honey-comb-work of its operation shall have been 
broken of by the violence of the waves, that a further ex- 
tension of its ravages can be apprehended : a circumstance 
which may he prevented by occasionally throwing along 
the face of the structure, fragments of mineral substances, 
as iron or copper; the poison of which would be fatal to 
the Animals. Their operation is not observed to extend 
much below the low water mark. The manner in whim* 
these burrowing Mollusks effect their operation on t»® 
solid rock, has been the subject of controversy, an 
perhaps may differ in the different families. It is certain 
that the Terediu.es efl’ect the destruction of wood by th e 
