149 



LETTER X. 



THE BORING MOLLUSCA AND NEST-BUILDERS. 



I must now beat back a little, having been led, almost 

 inadvertently, to pass unnoticed a tribe nearly allied to the 

 burrowers in sand and gravel, but of deeper interest. The 

 tribe in question are almost exclusively Bivalves, and, to 

 secure themselves, they excavate their cells in solid bodies, 

 — in wood, hardened clay, and harder rocks, — whence they 

 cannot again issue or be removed; their house during life, 

 and after death, their grave. The Teredo bores his long 

 tortuous cell in wood ; the Pholades construct their more 

 capacious dwellings in wood and in clay ; the Lithodomi and 

 Saxicavae excavate limestone rocks, coral-reefs, and the 

 thick shells of other mollusks; while the Fistulanae and Clav- 

 agellas are said to bore indifferently into sand, wood, rocks, 

 and into shells. In general, each species confines itself to 

 one kind of substance, but this is not always the case. 

 Olivi says, that he has twice seen Pholades in a piece of 

 compact lava ;* the common European species of that 

 family are found as often in timber as in clay, and some 

 of them perforate likewise calcareous rocks. Montagu tells 

 us, he had specimens of Gastrochaena modiolina in common 

 limestone, in fluor, and in granite ; -j- and Dr. Pulteney 

 speaks of Venerupis irus as being plentiful on the Dorset 

 coast in clay as well as in limestone. J — They are to be found 

 on all shores, from Greenland to the furthest Ind. Within 

 the tropics, however, they are most abundant, and of the 

 largest size; but the station most celebrated in history is 

 European, viz. in the Bay of Naples, near to Pozzuolo, 

 where a colony of Lithodomi § had settled themselves in 

 the pillars of the temple of Jupiter Serapis during the period 



* There is probably some error in this observation, so far as it would lead 

 to t lie inference that the Pholas had bored into the lava. Spallanzani, who 

 tells us that he had given particular attention to the subject, never observed 

 the lithophagous molluscs to u make their lodgments but in calcareous 

 stones." — Trav. in the Two Sicilies, i. 178. 



t Test. Brit. Supp. 25. % Ibid. 109. 



§ Bohadtch says they are Pholades which have made these excavations. — 

 An. Marin. 154. But this is a mere licence of nomenclature : the species 

 is the Mytilus lithophagus, Li/j«.=Modiola lithophaga, Lam. 



