MULTI VALVES PHOLAS. 21 



that in many instances, they might be considered as mere 

 varieties rather than different species; however, they alt 

 possess sufficient determinate characters, to prevent ;>n y 

 admixture with the genera of Bivalves. 



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

 long, wliich is constituted by two large valves, being si- 

 tuated opposite to each other, and to which is attached, 

 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 ofthc 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 pe- 

 culiarity 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. 



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

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

 frequently seen witliout the accessory valves, the young collector 

 niiglit, under such circumstances, lie deceived, and be induced to 

 place them amonij the Bivalves, instead ol'tlie jMuItivalves. 



