222 EXPLANATION OF TERMS. 



the middle, and tapering to each end ; 



from fusis, a spindle. 

 Fluviatile. Belonging to fresh water ; from 



fluvms, a river. 

 Globose, Globular. Approaching the form of a 



glohe. 

 Genus. A separate family, distinguished from all 



others by certain permanent marks, called 



generic characters : from gen us, a kind. 

 Gibbous. Convex, swelling out, from gibbus, a 



swelling, a hunch on the back. 

 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 iridescere, to shine like a 



rainbow, in Latin iris. 



Interstice. Space between one part and another. 

 Inequivalve. Having unequal valves ; from in, 



not, equ us, equal, and valve. 

 Inequilateral. Having sides not uniform ; from 



in, not, equws, equal, and latera, sides. 

 Involuted. Rolled inwards ; from involut us, 



rolled up in. 

 Littoral. Belonging to the shore ; from litt us, 



a shore. 



Lateral. At the sides ; from later a, sides. 

 Longitudinal. In the direction of the length of 



a shell ; (i.e.) from the apex to the base. 



