Multispiral. Consisting of many whorls, as some fresh-water snails. 



Nacreous. Pearly or iridescent, as the interior of some Unios. 



Nave. The interior coating of Pisidium and Sphaerium. 



Nepionic. The second stage of the embryonic shell, as the glochidium of Unio. 



Nodulous. Provided with small knobs or projections, as the surface of some 



Unios. 



Notched. Nicked or indented, as the anterior canal of some gastropods. 

 Nucleus. The first part or beginning, as the apex in a univalve and the unibo 



in bivalves. 



Nucleated. Having a nucleus. 

 Obcouic. In the form of a reversed cone. 

 Oblique. Slanting, as the aperture of some shells when not parallel to the 



longitudinal axis. 



Oblong. Longer than high, as some Unios. 

 Obovate. Eeversed ovate, as some shells when the diameter is greater near the 



upper than at the lower part. 



Obtuse. Dull or blunt, as the apex of some univalves. 

 Olfactory. Pertaining to the smell. 

 Olivaceous. "Colored like an olive. 

 Opisthodetic. With the ligament behind the umbones. 

 Orbicular. Like an orb or disk, as some Sphaeria. 

 Organism. An organized being, or living object made up of organs. 

 Ovate. Egg-shaped. 

 Ovately conic. Shaped like an egg, but with a somewhat conic apex, as some 



univalves. 



Oviparous. Bringing forth young in an egg which is hatched after it is laid. 

 Ovisac. A pouch in which the eggs or embryos are contained. 

 Ovoviviparous. In this case the young are formed in an egg but are hatched 



inside the parent. 



Papillose. Covered with many little bulgings or pimples. 

 Parallel. Having the same relative distance in all parts, as when the spiral lines 



in univalve shells are the same distance apart all the way around. 

 Parivincular. A ligament " which may be compared to a cylinder split on one 



side, attached by the several edges, one edge to each valve." 

 Patelliform. Shaped like a flattened out cone, as an Ancylus. 

 Patulous. Open and spreading, as the aperture in some univalves. 

 Paucispiral. Only slightly spiral, as some opercula. 

 Pearly. Having a substance like pearl, as the interior of Unio. 

 Pectinate. Like the teeth of a comb, as the gills of some mollusks. 

 Pedal. Pertaining to the foot. 



Pedunculated. Supported on a stem or stalk, as the eyes of land snails. 

 Pelagic. Living in the open sea, away from the shore. 

 Pellucid. Transparent or clear, as the shells of some snails; e. g., Vitrea. 

 Penultimate. The whorl before the last in univalve shells. 



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