llV A DICTIONARY OF TERMS. 



Edge. - - - See Margin. 



Epidermis. - An outer skin, or membrane, which covers the 

 surface of the majority of shells, and is, generally, 

 very tenaceous. Some shells, such as the Cow- 

 ries, and the Cones, are without an epidermis. 



Equilateral. The valves of bivalve shells are equilateral when 

 they precisely resemble each other in size and 

 form. 



Eouivalve. - When the two valves are pefectly alike. The 

 Muscles and Cockles, are equivalve shells. 



F. 



Fente. - - - The slit, or opening, which appears on the slopes 

 of bivalve shells, near the hinge, when the valves 

 are closed. 



Fissure. - - A notch, or slit. The slit limpet, Patella Jissura, 

 is an example. 



Fosset. - - The cavity containing the ligament. The fossets 

 are placed at the hinge in some bivalves. 



Fosset. - - The teeth of the hinge in bivalves, are also re- 



ceived into fossets, or cavities, in the opposite 

 valve. 



Furrow. - - A gutter, or groove, which when bivalves are 

 closed, runs along parallel to the hinge. 



G. 



Gapers. - - Shells whose valves never shut close. The Solens 



are gapers, at both ends, the Mya gape at one 



end only. 

 Gibbous. - - Protuberant. Some species of Murex are gibbous. 

 Glabrous. - Smooth, uniformly polished. 

 Grained. - - Dotted with small tubercles. 

 Groove. - - A hollow prolonged line, placed between two 



ridges. Cockles are grooved. 

 Group. - - The union of several shells that adhere together. 



The Oysters, and the Barnacles, form in groups. 



