58 
MARINE FAUNA OF ST. ANDREWS. 
only uses to which some of the other mollusks are applied are 
in the amateur manufacture of ornaments, such as shell pin¬ 
cushions from various univalves and bivalves, bracelets from 
Nassa incrassata and Trochus cinerarius , after the latter has 
had its nacreous layer exposed by an acid. 
The rock-boring shell-fish are five in number, though only 
one exercises any great influence on the disintegration of the 
rocks—viz. Pholas crispata , which often swarms in the shale 
and sandstone, and takes the place of the Pliolas dactylus of 
the chalk rocks of the south. Pholas Candida occurs too rarely 
to require special mention in this respect; and the same may 
be said of Saxicava ruyosa. The excavations of Patella vul- 
gata and Chiton fascicularis in sandstone show that no special 
boring-organ is necessary for this purpose. The latter species 
sometimes scoops out considerable cavities in sandstone, in 
which it reposes. The only wood-borer is Xylopliaga dorsalis. 
In taking, under this head, a general survey of the boring 
forms, it is found that they belong to at least three invertebrate 
subkingdoms, viz. the Protozoa, Mollusca, and Annulosa. In 
the first are boring sponges ; in the second, Bryozoa and various 
mollusks; in the third, sea-urchins, gephyreans, annelids, and 
cirripedes. 
The sponges appear to bore only into calcareous substances, 
such as shells and limestone. The Bryozoa perforate shells ; 
the mollusks proper, limestone, sandstone, aluminous shale, 
gneiss and other rocks, wood, wax, shells, &c.; the annelids 
tunnel shells and rocks of various kinds ; the sea-urchins cal¬ 
careous rocks, gneiss, granite, and other rocks ; the gephyreans 
and cirripedes shells and limestone. Good opportunities are 
afforded at St. Andrews for studying the boring-action of the 
mollusks and annelids. Pholas cvispata and Leucodore ciliata 
are equally abundant, and must exercise as much influence 
on the disintegration of the sandstone and shale between tide- 
marks as the boring sponges amongst the shells in deep water; 
while Patella , Chiton , Saxicava , and Dodecaceria are also 
frequent. 
The theories which have been promulgated to explain the 
mode by which these various creatures perforate materials so 
diverse may be ranged round two great centres, viz. the 
