PEDUM. 259 



The shell pertaining to this beautiful family of moUusks 

 is either free or attached by one valve : it is often inequivalve, 

 somewhat irregular, and generally auriculated at the base on 

 each side. The ligament is either internal or semi-internal, 

 inserted in a central pit or groove, and the animal is not 

 always provided with a byssus. 



Five genera pertain to this family — 'Pedum , Lima, Fecten, 

 Plicatula, and Sjwndi/lus. 



The organization of the Pedum is intermediate between 

 that of Aviciila and Spondylus. Like the former it is pro- 

 vided with a strong tendinous byssus, exserted in the same 

 direction, and the shell, like that of the latter, no longer 

 exhibits a particular fibro-laminar structure, but forms a 

 solid umbonal area. Its habits, however, differ considerably 

 from both, as many of the family are found partially buried 

 in madrepores, or in crevices of their own boring. 



The naturalist has much to learn respecting the uses and 

 relative construction of these singular mollusks. They dwell 

 beneath the waters, and he may look with prying eyes on 

 their retired abodes without discovering either their going 

 out or coming in, or yet the means by which they obtain 

 their food. Thus much we know% however, that the world 

 of waters teems with delighted existence ; that tiny mollusks 



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