402 SHELLS AND SHELL-FISH. 



Striated. Marked with lines, either elevated or raised, 

 at parallel and nearly equal distances. Such marks 

 are termed^ striae only when they are very slender, 

 not much exceeding the hreadth of a hair, or at most 

 of the human nail : when they are deeper and in- 

 dented, they are termed grooves ; or, if elevated, 

 ridges. Sometimes the striae are formed by a series 

 of punctures, as in Mitra cardinalis, &c. ; while in 

 other instances they are elevated and granulated, as 

 Mitra granulosa. In bivalve shells they are almost 

 always concentric, or following parallel to the outer 

 margin. All these variations have been found of 

 great importance in the determination of species, and 

 hence require the closest attention. 



Suh. Nearly or partially, as sub-striate, sub-fusi- 

 form, &c. 



Subulate. Awl-shaped, long, slender, and acutely 

 pointed, as Terehra, Turritella, &c. 



Sulcated. Broad grooves, sunk beneath the surround- 

 ing surface. 



Suture. A term applied to the line of junction in the 

 whorls of spiral shells, or that where two parts join 

 or fit into each other. 



Symmetrical. Where the two sides of a shell are alike. 



Terehrating Testacea are such as take up their habi- 

 tations in other substances, as Pholas, &c. 



Tessellated. Divided into squares or chequers, either 

 by a division of the colours, or by the crossing of the 

 striae. 



Transverse. A line di-awn across the breadth of a shell. 

 Thus the coronations of the Volutes are transverse, 

 so also are the bands on the AcliatincB, and all those 

 upon bivalve shells which radiate from the bosses. 



Trigonal or triangular. Having three equal or unequal 

 sides, as Donax, Hyria, Cardlssa, &c. 



Trilobate. Divided into three obtuse divisions or lobes. 



