GLOSSARY. XI 



Lunar or Lunate, having a crescent form. 



Mar$rirt,theedgeof the shelh anterior, the space in which 

 the hgament is situated: posterior, the space on the 

 other side of the hinge: superior, the space between 

 the anterior and posterior parts. 



Marginate, (in Univalves), having the sides of the shell 

 thickened: (in Bivalves), surrounded with an elevated 

 margin. 



Mouth, see Aperture. 



Muscular Impressions, are the marks made by the mus- 

 cles with which the animal adheres to the shell, as in 

 the Common Oyster. 



Obovate, nearly oval. 



Obsolete, obliterated. 



Obtuse, blunt pointed. 



Operculum, (in Multivalves), the stellular valves which 

 shut up the superior orifice: (in Univalves), the part 

 which exactly fits into the aperture, and encloses the 

 animal. 



Papillary^ having the apex rounded. 



Papyraceous, of the thinness of paper. 



Patulous, gaping. 



Pectinated, when the longitudinal ribs on the anterior sur- 

 face form acute angles with the transverse striae. 



Peduncle, a tendinous substance belonging to some of the 

 Multivalves, by means of which they adhere to solid 

 bodies. 



Pillar, see Columella. 



Pillar-lip, that side of the aperture in which the columel- 

 la is situated. 



Pisiform, pea-like. 



