PECTEN. 



GENERIC CHARACTER. 



Shell bivalve, free, regular, inequivalve, eared ; 

 beaks contiguous. Hinge toothless, with a trigo- 

 nal pit for the cartilage. One muscular impres- 

 sion. 



OBSERVATIONS. 



Most of the shells of this perfectly natural and 

 extensive genus are distinguished by their elegant- 

 ly coloured markings, which are frequently ex- 

 tremely variable in the same species. They are 

 all inequivalve, having one valve more convex than 

 the other, although in a few instances the variation 

 is scarcely perceptible. The inferior or lower 

 valve is generally less coloured than the superior, 

 and this character, together with the deeper sinus 

 of the ear, will easily distinguish it from the othei*. 

 Nearly all the species have either ribs or striae, ra- 

 diating from the beaks, and this, in connexion with 

 their peculiar form, has originated the vulgar name 

 of fans. The habits of the animal, and the regula- 

 rity in shape, together with the substance of the 

 shells, which are never of a coarse laminar struc- 

 ture, widely remove them from the oysters, with 

 which they were confounded by Linnaeus. 



A byssus has been observed, in several species 

 of this genus, to pass under the ear of the inferior 

 valve, and they are by this slender process attached 

 to rocks in deep water, but never, as the Mytili 

 frequently are, to floating substances : others 



