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-fisli 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 Pholas 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 rugosa. 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 Xylophaga 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, MoUusca, 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 roc^s, 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 crispata 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 



