MULTIVALVES. — PHOLAS. 33 



sess sufficient determinate characters to prevent any admix- 

 ture with the genera of Bivalves. 



The form of the Pholas is in most species ovate or ob- 

 long, which is constituted by two large valves, being situat- 

 ed opposite to each other, and to which is attached, in the 

 vicinity of the beaks, a number of smaller ones, serving as 

 substitutes for a hinge, which, in bivalves, or shells of two 

 opposite parts only, determines their generic character. 



Another character of the Pholas is, that the valves, (i. e. 

 the two large ones), never shut close, they are invariably 

 open at one end, and, in most instances, at both. 



In the interior of the shell, in each valve, nearly under 

 the beak, is an incurved tooth, sometimes of considerable 

 length, and which may certainly be considered as a pecu- 

 liarity of the genus. 



The exterior of the Pholas is generally destitute of colour ; 

 sometimes it partakes of a brownish cast, but the shell is 

 usually of a pure or dusky-white : however, the absence of 

 colour is amply compensated for by the beautiful fret-work 

 with which the shells of this genus are adorned. 



In some species the reticulations are so delicate in their 

 fabric, as to resemble the finest lace ; in others the texture 

 is coarser, and approaches nearer to small basket-work; 

 and in the Pholas costata the shell is covered with regular, 

 elevated, jagged, or scolloped ribs, so elegantly disposed, 

 as to render it no less desirable for its beauty than its scar- 

 city. 



The Pholades are found in company, but not in groups 

 or clusters, as the Lepades are ; for each individual Pholas 

 is detached from its neighbour, and occupies a separate and 

 distinct habitation, which it forms for itself, by expressing 

 a corroding juice, in any substance Avhich accident or intent 

 has made most eligible. 



Stone, clay, wood, sponge, and coral, equally serve as ha- 

 c3 



