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A DICTIONARY OF TERMS. 



Testacea. - 



Tiled. - - ■ 



Transverse. • 



Tricuspidate. 



Trifid. - - - 

 Trilobed. - ■ 

 Tubercle. 



Turban. 



Turn. 



All animals of the class Mollusca, which are 

 covered with a solid roof of carbonate of lime, 

 come under the denomination of Testacea. 



See Imbricated. 



Across. Bands, or striae, running across a shell, 

 are called transverse. 



A shell armed with three short points. The 

 Anomia tridentata is an example. 



Slit into three. A trifid tooth. 



Having three lobes. 



A protuberance, or knob, raised on the surface 

 of some shells. Several species of the genus 

 Murex, are loaded with tubercles. 



All the whirls, or spires, of a Univalve, taken 

 collectively, are called the turban. The Helix 

 planorbis, has a fiat turban ; the Trochus tuber- 

 culatus a short turban, and the Trochus Zizi- 

 phinus a produced turban. 



The turn of a spire, is a single, but complete 

 revolution. In the Nautilus, the last turn of the 

 spire envelopes all the others. 



U. 



Umbo. - - - The same as summit, 



Umbilicus. - A small hole at the bottom of some Univalve 



shells, formed in the thickness of the columella, 



or pillar. 

 Undulated. - Waved. 

 Unilocular. - This term is used for Univalves, that have but one 



chamber. The Paper Nautilus, the Cowries, 



the Olives, &c. are unilocular shells. 

 Un i valve. - A division of shells, composed of but one valve, or 



piece. 



V. 

 Valve. - - - The testaceous covering of the Mollusca. When 



of a single piece, the shell is called Univalve ; 



when of two pieces, Bivalve ; and when formed 



of more parts than two, Muliivalve. 



