180 AMERICAN MARINE CONCIIOLOGY. 



Genus PECTUNCULTJS, Lam. 

 Syst. 115. 1801. 



Animal with a largo crescent-shaped foot, margins of the sole 

 undulated ; mantle open ; margins simple, with minute ocelli ; gills 

 equal, lips continuous with the gills. 



About sixty species known, ranging from 8 to over 100 fathoms. 



1. P. pennaceus, Lamarck. Fig. 173. 



Aniin. sans Vert. 

 P. Uneatus, Reeve Zool. Proc. 1843. 

 P. spadiceus, Reeve, Zool. Proc. 1843. 



Shell orbicular, swollen, decussately -striated, longitudinal striae 

 the strongest; whitish, irregularly painted with large and small 

 dark-brown spots and streaks; umbones bent inwards to the an- 

 terior end of the ligament. 



iV. Carolina to West Indies. 



This shell has been doubtfully referred by some conchologists 

 to P. Chdrlestoniensis, a post-pliocene fossil of S. Carolina. 



Genus NUCULA, Lamarck. 

 Syst. 115. 1801. 



Animal with the mantle open, its margins plain; foot large, 

 deeply fissured in front, forming when expanded a disk with ser- 

 rated margins; mouth and lips minute, palpi very large, rounded, 

 strongly plaited inside, and furnished with a long convoluted ap- 

 pendage ; gills small, plume-like, united behind the foot to the 

 branchial septum. 



Distribution about 10 species, from 5 to 100 fathoms. 



1. N. tenuis, Montagu. Fig. 478. 



Test. Brit. Suppl. 56, t. 29, f. 1. 1808. 



Shell small, thin, trapezoidal ; smooth, without radiating lines ; 



beaks prominent; epidermis grass-green; inner margin entire. 



Length 7.5, height 6.25 mill. 



Maine, northwards. (Eur.) 



2. X. proxima, Say. Figs. 479, 480. 



Journ. Philad. Acad., ii. 270. 1822. 

 Area nucleus, Linn (part). Syst. Nat., edit. xii. 1143. 



Shell oblique, ovate-triangular, crossed by minute concentric 

 and radiating lines; epidermis olivaceous; margin crenulated; 

 hinge-teeth large, twelve before and eighteen behind the beaks. 

 Length 11, height 9 mill. 



Whole Coast, southwards to N. Car. {Eur.) 



