EXPLANATION OF TERMS. 



357 



Sinuous. Waved. 

 Sinus. A gutter, or curvature. 

 Siphon. A fleshy pipe. 

 Siphuncle. A siphon, or tube. 

 Spathulate. Spoon-shaped. 



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. 



Stellated. With rays like a star. 



Striated. Marked with lines, either raised or not, at parallel and 

 nearly equal distances. 



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

 form), &c. 



Subulate. Awl-shaped. 



Sustentacula. Under tentacula. 



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

 wrapping over each other. 



Tentacula. Arms or feelers. 



Terebrating Testacea. Such as take up their habitations in other 



substances, as Pholas, &c. 

 Testaceous. Composed of the materials which constitute shell. 

 Transverse. See Longitudinal. 

 Truncated. Cut short off, or ending abruptly. 

 Tuberculated. Covered with small protuberances. 

 Turbinate. Having the body of the shell large or swollen, and the 



spire comparatively short. 

 Turreted. Having the whorls gradually decreasing, so as to form a 



fine point at the apex. 



Umbilicus. A small hollow, or sometimes a deep hole, on the side of 

 the inner lip in spiral shells, formed by the inner edges of the 

 whorls not touching each other : in some genera, as Scalaria and 

 Solarium, it is so deep as to extend to the apex of the shell; in 

 others, as Trochus, it is small; in Bidimus it becomes nearly 



