GLOSSARY. 77 



Lateral. The lateral teeth take their rise near the umbones, 

 and proceed towards the sides of the shell. 



Ligament. The external substance by which the two valves 

 of bivalve shells are connected. 



Lip. The inner lip, or labium, is used to express that side 

 of the aperture nearest to the axis ; the outer lip, or 

 labrum, is the edge of the aperture at the greatest dis- 

 tance from the axis. 



Longitudinal. Lengthwise. Longitudinal striae, &c. 



Mantle. The cutaneous and fleshy envelope which invests 

 the interior of the shell of conchifera ; in Limaces the 

 external fleshy substance covering the shell, sometimes 

 called the shield. 



Marginated. Having an edge or border thicker than the 

 rest. 



Nucleus. A kernel. Anything forming a centre round 

 which matter is gathered. The nucleus of a shell is 

 the first part formed ; generally applied to the apex of 

 spiral shells. 



Oblique. In a slanting direction. The whorls of spiral 

 univalves generally take an oblique direction, in refer- 

 ence to the imaginary axis of the shell. 



Obsolete. Used to express an indistinctness of character. 



Obtuse. Blunt ; generally used to express the character ol 

 the spire. 



Operculum. The plate which serves to protect the aperture 

 in some mollusks. 



Patelliform. Shaped like a disk. 



Pedicle or Peduncle. The stem or organ of attachment of 

 some water-shells 



Pellucid. Clear and somewhat transparent. 



Periostraca. The natural epidermis or thin skin which 

 covers some shells. 



Peristome. The lip or rim that surrounds the aperture of 

 most univalves. 



Pillar. The name of the column which forms the axis of 

 spiral shells, round which the whole revolves. 



Plait or Fold. A term generally applied to the promi- 

 nences on the inner lip of some univalve shells. 



Posterior. The posterior, or hinder part of a bivalve shell, 

 is that in which the siphonal tube of the animal is 

 placed. 



