356 



POPULAR CONCHOLOGY. 



called obsolete strise, not because they are worn off by accident, 



but because they are only rudimentary, or very slightly developed. 

 Operculum. A hard shelly or horny lid, which covers the aperture of 



many spiral shells, and is attached to the foot of the animal. (See 



Epiphragma.) 

 Orbicular. Quite round. 

 Ovate. Egg-shaped. 



Papyraceous. Excessively thin, like paper. 



Peduncle. A stalk, or support. 



Pelagic. Belonging to, or found in, deep seas. 



Perforated. Having holes (as the Terebratula) in the boss, and also 



in the substance of the shell. 

 Peritreme. The entire edge of the aperture, embracing both lips. 

 Persistent. Lasting, not falling off. 



Phosphorescent Shining in the dark, like the glow-worm. 

 Plaits. Folds, or raised lines on the Columella. 

 Planorbicular. Flat, and orbicular. 

 Polythalamous. Having many chambers. 

 Posteally. At the back, behind. 



Posterior. The side of the shell in Bivalves, opposite to that on 



which the ligament is placed. (See Anterior.) 

 Punctured. Pierced with small holes. 



Recurved. Turned backwards. The canal of some species of the 

 genera Strombus and Cerithium is remarkably so. 



Reflected. Turned or folded backwards, as in the thickened lip of 

 the common Helix. 



Retractile. Capable of being drawn backwards. 



Retuse. When a spiral shell is retuse, the inner whorls appear to have 

 been pressed into the body of the shell, and the apex is below the 

 level of the last whorl. 



Reversed. The same as sinistral. (See Sinistral.') 



Rhombic. Quadrangular, four-sided. 



Septum. A division. 



Serrated. Edged like a saw. 



Sessile. Attached, without a stalk or peduncle. 



Setaceous. Bristly with hairs. 



Sinistral. Having the aperture on the left side, as opposed to dextral 

 (see Dextral), also called reversed. 



