296 POPULAR BRITISH CONCHOLOGY. 



Murices ; imtelliform, shaped like a dish^ or limpet. The 

 pemiUimate tvJiorl is the last whorl of the spire previous to 

 that which forms the body of the shell. The words plicated, 

 or folded ; polygonal, or many-sided ; ineqiiivalve, or with 

 one valve exceeding the other ; pijriform,, or pear-shaped ; 

 jpyraimdal, or spine-like; tessellated, or coloured in pat- 

 tern like a tessellated pavement ; tuhercidated, or knobbed ; 

 turgid and ventricose, or swelled and bulky ; t arreted, or 

 rising by angular gradations like turrets; iimlilicated, or 

 having a hollow or circular depression ; and auriculated, 

 having prominent flattened processes, — are easily applied, 

 as well as many others which are not used exclusively in 

 conchology. 



The remaining terms apply to the habits and structure of 

 the moUusca and their shells. 



When the mollusc is locomotive, and the shell conse- 

 quently not fixed to any spot, it is said to hQ free. When, 

 on the contrary, the shell is fixed, it is described as attached. 

 The attachment takes place either by means of a portion of 

 the shell (in bivalves, one valve) growing to the surface of 

 rocks or other shells ; or by means of a hyssus, or bunch of 

 fibres. The oysters are often attached in the former manner ; 

 while mussels and Finnce ride at anchor by the latter method. 



