EXPLANATION OF TERMS. 217 



Testaceous. Composed of the materials which 

 form shells; from the Latin testa, a 

 shell. 



Tentacula. The feelers of the mollusca ; from 

 the Latin tent o, I try. 



Turbinate. The body swelling, and spire com- 

 paratively small ; from the Latin turbin is, 

 of a whirlwind. 



Turreted. The whorls gradually decreasing to 

 a fine point ; the length of turreted shells 

 greatly exceeds their breadth. 



Teeth. The pointed protuberances at the hinge 

 of Bivalve shells ; the cardinal or central 

 teeth are those situated on the hinge ; the 

 lateral teeth are those at the sides of the 

 hinge, and are often remote. 



Tuberculated. Covered with tubercles, or small 

 protuberances. 



Tortuous. Twisted; from the Latin tort us, 

 twisted. 



Umboncs, or Bosses. The swelling part of bivalve 

 shells near the beaks ; from umbo, the 

 boss of a shield. The highest points of 

 these are considered the summits. 



Umbilicus. A small hollow at the base of the 

 columella, visible underneath. 



Undulating. Wave-like; from undula, a little 

 wave. 



Univalve. A shell composed of one valve; from 

 un us, one, and valve. 



Volutions, or Whorls. The distinct turns of the 

 spire. 



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