172 AMERICAN MARINE CONCHOLOGY. 
Genus MONTACUTA, Turton. 
Conch. Dict., 102. 1819. 
1. M. ELEVATA, Stimpson. Fig. 440. 
Shells New Eng., 16. 1851. 
Montacula bidentata, Gould (non Auct.), Invert. Mass., edit. i. 59. 1841, 
Shell ovate, triangular, beaks tumid, elevated, nearly central, 
disk flattened below the middle; tooth on the shorter side oblique 
and excavated for the reception of the ligament. White, under a 
very thin straw-colored epidermis. 
Length 5, height 4 mill. 
New England. 
2. M. Gounp1, Thomson. Fig. 441. 
Am. Journ. Conch., iii. 33, t. 1, f. 15. 1867. 
Shell minute, diaphanous, rhomboidal, inequilateral, not com- 
pressed. Beaks rather prominent, not in contact, with an exca- 
vated areola infront. Basal margin nearly straight, ends obtusely 
rounded, forming a rhomboidal outline; lines of growth regular, 
with an opaque white thickened band surrounding the margin; 
hinge with the cartilage occupying a pit between two rather strong 
teeth. 
New Bedford, Mass. 
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Genus LEPTON, Turton. : 
Brit. Bivalves, 62. 1819. 
The mantle is much produced beyond the margin of the shell, 
and is furnished with slender, tentacular filaments. The foot is 
folded as in Arca, but when the animal is in motion it forms an 
expanded disk. 
1. L. LEPIDUM, Say. Fig. 461. 
(Amphidesma.) Journ. Philad. Acad., v. 221. 1826. 
Shell very much compressed, subtriangular, remarkably thin, 
pellucid, equilateral, somewhat iridescent, with numerous con- 
centric wrinkles, and equally numerous, very minute, regular, 
longitudinal strie, curving towards the anterior and posterior 
edges ; cardinal teeth obsolete, laterals prominent. 
Length 6, height 6.5 mill. 
South Carolina. 
2. L. LONGIPES, Stimpson. 
Bost. Proc., y. 111. 1855. 
Shell subtriangular, somewhat rounded, slightly compressed, 
