EXPLANATION OF TERMS. 



299 



that on which the ligament is placed. (See An- 

 terior.) 



Recurved. Turned backwards. The canal of some of 

 the genera Strombus and Cerithium is remarkably so. 



Reflected. Turned or folded backwards, as in the thick- 

 ened lip of the common Helix. 



Retractile. Capable of being drawn backwards. 



Retuse. When a spiral shell is retuse, the inner whorls 

 appear to have been pressed into the body of the shell, 

 and the apex is below the level of the last whorl. 



Reversed. The same as sinistral. (See Sinistral.) 



Sessile. Attached to any body, without a stalk or pe- 

 duncle. 



Sinistral. Having the aperture on the left side, as op- 

 posed to dextral (see DeoctraP), also called reversed. 

 Sinuons. Waved. 



Sinus. A gutter, or curvature, in the lip of Univalves. 

 Siphon. A fleshy sucker. 



Spire. Those volutions of a spiral shell which are above 

 the lowest or body whorl collectively form the spire 

 of the shell, whatever shape it may assume. The 

 variations in the form of this part are numerous. In 

 some it is excessively lengthened ; in others it is not 

 even raised above the body whorl. In Planorbis the 

 spire is sunk, while in Cyprcea it is so small as only 

 to be seen when the shell is young, after which it is 

 covered over by the enlargement of the body whorl 

 or principal volution. 



Striated. Marked with lines, either elevated or raised, 

 at parallel and nearly equal distances. 



Sub. Almost, or approaching to ; as sub-fusiform (nearly 

 fusiform), &c. 



Sutures. The corkscrew line formed in the spire, by the 

 whorls wrapping over each other. 



