MARINE MOLLUSCA OF THE UNITED STATES. 18] 
3. N. EXPANSA, Reeve. Figs. 481, 482. 
Belcher’s Arctic Voy. 897, t. 33, f. 2. 1855. 
N. Bellotii, Adams, Zool. Proc. 51. 1856. 
Shell large, ovate-triangular, tumid, the surface distinctly nu- 
cleated wiih ridges, both dorsal areas with fine radiating strie; 
ten teeth in front and fifteen behind the beaks. Dark chestnut 
colored. q 
Length 14, height 9 mill. 
Canadian waters, northward. (Hur.) 
This may be only a very large flourishing state of WV. tenuis. 
4, N. inFLaATA, Hancock. Figs. 483, 484. 
Ann. Nat. Hist. 333, t. 5, f 18,14. 1846. 
Shell trapeziform, inflated, thin, coarsely concentrically striate ; 
intefior margin simple; hinge with five teeth before and ten 
behind the large oblique ligament cavity; epidermis yellowish- 
green. 
Length 7.5, height 6.25 mill. 
Labrador, northwards. 
5. N. DELPHINODONTA, Mighels. Figs. 485-487. 
Bost. Journ. Nat. Hist., iv. 40, t..4, f. 5. 1842. 
Shell minute, obliquely triangular, beaks raised, nearly terminal ; 
hinge with three anterior and seven posterior teeth ; epidermis 
olivaceous. 
Length 3.25, height 2.75 mill. 
New England, northwgrds. 
Undetermined Species. 
N. RapDIATA, De Kay. Moll. N. York 179, t. 12, f. 216. 1843. 
Dredged in E. River, N. Y. The figure is not recognizable. 
Genus LEDA, Schumacher. 
Essai Noy. Syst. 1817. 
The animal is furnished with two partially united, slender, un- 
equal siphonal tubes; gills narrow, plume-like, deeply laminated, 
attached throughout; mantle-margin with small ventral lobes, 
forming by their apposition a third siphon. 
The typical group comprises about 80 species, inhabiting Arctic 
and northern seas, 10 to 180 fathoms. 
1. L. renutsuLtcatTa, Couthouy. Figs. 488, 489. 
(Nucula.) Bost. Journ. Nat. Hist., ii. 64, t. 3, f. 8. 1838. 
Nucula minuta, Gould, Invert. Mass., edit. i. 101. 1841, 
Shell ovate-lanceolate, produced, narrowed and rostrated behind, 
