216 EXPLANATION OF TERMS. 



Rugose. Rough or wrinkled ; from rug a, a 

 wrinkle. 



Retractile. Capable of being drawn back ; from 

 re, back, and tract us, drawn. 



Reticulated. Crossed like net work ; from re- 

 ticul um, a small net. 



Revolute. Rolled back; from re, back; and 

 volut us, rolled. 



Spire. The upper whorls collectively; from the 

 Greek p (speir) convolutions gradu- 

 ally increasing in diameter. 



Suture. The circular line of the spire, where 

 one volution meets another ; from sutur a, 

 a seam. 



Species. The subdivision of a genus, and dis- 

 tinguished from all others of the genus by 

 permanent marks called specific charac- 

 ters. 



Striated. Marked with fine striae, or lines, 

 either hollow or raised ; from stria, a stripe. 



Sinus. A gutter, or curvature ; from sin us, a 

 curved line. 



Subulate. Tapering, or pointed; from subul cr, a 

 pointed tool. 



Sides. The right side of a univalve is that 

 opposite the right hand of the person 

 looking at it, when the shell is placed 

 on its base with the aperture in front : 

 the left side is that opposite the left 

 hand, the shell being in the same position. 



Terrestrial. Belonging to the earth ; from terra, 

 earth. 



