96 PnOLADIDiE. 



approach existing times. Some of those now hving com- 

 menced their existence within our area as far hack as the 

 epoch of the coralline crag. Extinct, like recent species, 

 lived in cavities excavated hy themselves, and fitting their 

 dimensions. 



All the species of Pholas are endowed with the remark- 

 ahle power of perforating various substances of considerable 

 hardness, such as stone, shale or wood ; some indifferently, 

 some selecting one or other for their habitations. They 

 are never naturally found free. This habit of boring is 

 common to the whole tribe of which Pholas is the type, 

 and is presented also by certain members of other tribes. 

 The majority of Lamellibranchiate Mollusca may be said 

 to be borers, so far as the power of burying themselves in 

 sand, clay, mud, or gravel, can give them a claim to such 

 appellation, but the boring of the Pholas^ Teredo^ Xylo- 

 pliaga^ Pholadidea, of the Gastrochtcna, and its allies, and 

 of certain species of MytUida, appears to be effected by 

 very different means. The question how the boring 

 mollusca excavate their dwelling-places has long been dis- 

 cussed, and is still at issue among naturalists ; and the 

 name Pholas, (from (pcoXzco, to bore,) was applied by the 

 ancients to certain shell-fish whose power of perforating 

 the solid rock attracted their notice. A shell-fish is men- 

 tioned by Athenffius under the name of Pholas, probably 

 not one of the members of the genus now so called, but 

 the LitJiodomus lithophagus, or date-shell, which is very 

 abundant in the seas of Greece, and used by the people for 

 food, whilst the true Pholades are very scarce in the 

 TEgean, and not likely to have attracted popular attention. 



The earliest observations made upon the boring of 

 Pholas were those by the celebrated Reaumur, one of the 

 most excellent of practical naturalists. They are published 



