lviii 



A DICTIONARY OF TERMS. 



Perforated. Pierced. The disk of the Haliotis, and the apex 



of the Patella Grceca, are perforated. 

 Pillar. - - The axis upon which the spires turn in Univalve 



shells. 

 Pisiform. - - Of a pea shape. 

 Plain. - - - Uniform, flat. The Anornia placenta, is a plain 



shell. 

 Plaited. - - Many Univalve shells are plaited on the columella, 



or pillar lip, which characterises their genera. 



The Volutes, are plaited. 

 Plaited. - - When the margins of a Bivalve shell deviate 



from a straight line, they sometimes form a plait. 



Thus one of the characters of the genus Tellen, 



is to have the anterior margin plaited. 

 Posterior. - That half from the hinge, in Bivalve shells, which 



does not show the cardinal ligament. 

 Pyriform. - - Pear-shaped. The Bulla Jicus is a pyriform shell. 



Q. 



Quadrivalve. Four-valved. The operculum of the Acorn shell 

 is quadrivalve. 



R. 



Reticulated. Like net-work. Many shells have their surfaces 



reticulated. 

 Ribs. - - - Protuberant striae on the surface of a shell. The 



Cockles are strongly ribbed. 

 Rostrum. - - See Beak. 

 Rugose. - - Wrinkled. The surfaces of some shells are 



rough, or wrinkled. The Tellina rugosa, is one 



among many examples. 



Scabrous. - Rough, rugged. The shells of the genus Chama 



have scabrous valves. 

 Serrated. - Toothed like a saw. Many Bivalve shells have 



their margins serrated, such as the Spondyles. 



