MULTIVALVES PHOLAS. 9 



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

 long, which is constituted by two large valves, being 

 situated opposite to each other, and to which is attach- 

 ed, in the vicinity of the beaks, a number of smaller ones, 

 which serve as substitutes for a hinge, which, in Bivalves, 

 or Shells of two opposite parts only, often determines 

 their generic character. 



It is from the circumstance of the Pholas possessing 

 more than two valves that it is distinguished, and, conse- 

 quently classed among the Multivalves or many shelled 

 genera, and not among the Bivalves or Shells of two 

 valves*. 



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

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

 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 mostly destitute of all co- 

 lor ; sometimes, however, it partakes of a brownish cast, 

 but, generally, the shell is of a calcareous appearance, 

 and either inclines to a pure or dusky-white, or else a 

 sort of blueish or yellowish-brown tint is spread over it: 

 however, the absence of color is amply compensated for 

 by the beautiful fret- work with which shells of this ge- 

 nus are adorned. 



* It was perhaps unnecessary to have been thus explicit, with 

 regard to this distinction; but as the Pholas is by no means ua- 

 frequently seen without the accessory valves, the young' collector 

 might, under such circumstances, be deceived, and be induced to 

 place them among the Bivalves, instead of the Multivalves. 



