Iviii 



A DICTIONARY OF TERMS. 



Perforated. 



Pillar. 



Pisiform. - 

 Plain. - - 



Plaited. - 

 Plaited. - - 



Posterior. 

 Pyriform. - 



Quadrivalve. 



Pierced. The disk of the Haliotis, and the apex 



of the Patella Grceca, are perforated. 

 The axis upon which the spires turn in Univalve 



shells. 

 Of a pea shape. 

 Uniform, flat. The Anomia placenta, is a plain 



shell. 

 Many Univalve shells are plaited on the columella, 



or pillar lip, which characterises their genera. 



The Volutes are 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. 

 That half from the hinge, in Bivalve shells, which 



does not show the cardinal ligament. 

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



Q. 



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. 



S. 



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. 



