168 AMERICAN MARINE CONCIIOLOGY. 



elongated within the pallial line, posterior oblonf 



oblique furrow. Lucina. 



Sliell globular, posterior side furrowed or angulated, vimboues much re- 

 curved ; lunule short or indistinct ; ligament to a certain extent external, 

 placed in a groove on the hinge-line, and outside the hinge-plate ; teeth 

 altogether wanting. Cryptodon. 



Shell suborbicular, smooth ; ligament double, rather long, submarginal ; 

 hinge-teeth 2.2, of which the anterior in the left valve and posterior in 

 the right, are bifid, lateral teeth none ; muscular impressions polished, 

 rounded. Mysia. 



Shell small, thin, suborbicular, closed ; beaks small ; margins smootli ; 

 ligament internal, interrupting the margin, or on the thickened margins ; 

 cardinal teeth 1 or 2, laterals 1-1 in each valve. Kellia. 



Shell oblong, inequilateral, anterior side very short ; ligament concealed 

 between the valves ; hinge-teeth 2-2. Tuktonia. 



Shell small, thin, oblong, anterior side longest; hinge line notched; liga- 

 ment internal, between two laminar diverging teeth. Montacuta. 



Shell equivalve, orbicular, subcquilateral, compressed, gaping slightly at 

 the sides ; surface of valves shagreened or smooth ; margins plain ; beaks 

 acute. Hinge composed of a pair of teeth-like lamiute on eacli side of a 

 triangular, central excision in one valve ; a primary apical tooth in front 

 of a subtriangular excision of the hinge-margin, and flanked on each side 

 by a sublateral lamina in the other. Pallial impressions simple. 



Lepton. 



Genus LUCINA, Bruguiere. 

 Encyc. Meth., t. 284. 1793. 



Animal with the mantle freely open below; siphonal orifices 

 simple; mouth minute, lips thin; gills single on each side, very 

 large and thick ; foot long, cylindrical, pointed, slightly heeled at 

 the base. 



1. L. filosa, Stimpson. Fig. 42G. 



Shells of New England, 17. ISol. 

 Luci7ia radula, Gould (not Montagu), Invert. ]\Iass., edit. i. 69. 1811. 

 Lucina contracta, De Kay (not Say), Xat. Hist. New York, 214, t. 27, f; 



275. 1843. 



Shell orbicular, depressed; surface with numerous remote con- 

 centric laminated striae; lunule depressed lanceolate; lateral teeth 

 obsolete. White or light brown. 



Length and height 1.5 inches. 



New Englnnd. 



