EXPLANATION OF TERMS. 213 



Emarginated. Notched, or having the margin 



excavated by a sinus. 

 Ferruginous. The colour of rust or iron-mould ; 



from ferrug o, iron rust. 

 Fusiform. Shaped like a spindle ; swollen in the 



middle, and tapering to each end ; from 



fusis, a spindle. 

 Fluviatile. Belonging to fresh water ; from flu- 



vi us, a river. 

 Genus. A separate family, distinguished from all 



others by certain permanent marks, 



called generic characters ; from gen us, a 



kind. 

 Gaping. The valves so partially closing, that 



the margins do not touch at every part of 



the circumference. 

 Imbricated. Lying one over another like the 



tiles of a house ; from imbrex, a tile. 

 Iridescent. Displaying the varied colours of the 



rainbow ; from irides cere, to shine like a 



rainbow, in Latin iris. 

 Ineqivalve. Having unequal valves; from in, 



not, equ us, equal, and valve. 

 Inequilateral. Having sides not uniform ; from 



in, not, equ us, equal, and latera, sides. 

 Involuted. Rolled inwards ; from involut ws, 



rolled up in. 

 Laminated. Having thin layers or scales called 



laminae. 

 Linear. Extremely narrow in proportion to its 



breadth, and of nearly equal diameter 



throughout. 

 Length. In Bivalves, the dimension extending 



