184 AMERICAN MARINE CONCHOLOGY. 
3. L. MYALIs, Couthouy. Fig. 499. - 
(Nucula.) Bost. Journ. Nat. Hist., ii. 61, t. 3, f. '7. 18388. 
Shell ovate, smooth, olive-colored; anterior part longest and 
rounded ; posteriorly acuminated and sub-rostrated ; teeth about 
12 on each side, sometimes increased to 16 or 18 in number. 
Length 27.5, height 17.5 mill. 
New England, northwards. 
This shell is higher in proportion to its width, and darker 
eclored than ZL. limatula; it also differs in the position of the 
beaks and number of teeth. 
4. L. opesaA, Stimpson. Figs. 500, 501. 
Proc. Bost. Nat. Hist., iv. 13. 1851. + 
Shell small, thin, inflated, oval, smooth; beaks nearly central; 
teeth small, 10 in front'and 12 behind; epidermis pale yellowish- 
green. 
Length 6, height 4 mill. 
(Deep-water.) Massachusetts Bay. 
Closely allied to Yoldia pygmea, Minst., but that sheil is more 
pointed and upturned at the posterior end. 
5. L. anorica, Gray. Figs. 502, 503. 
Nucula glacialis, Gray, Wood Index Test. Suppl., t. 2, f. 6. 
Nucula truncata, Brown, Brit. Conch. 84, t. 33, f. 18. 
Nucula Portlandiea, Hitchcock, Bost. Journ., i. 327. 
Nucula siliqua, Reeve, Belcher’s Arctic Voy., t. 33, f.°4. 1855. 
Shell oblong, ovate, ventricose; beaks prominent, nearly me- 
dian; posteriorly sulcate between two slight rounded elevations 
from beak to margin; 12 to 14 teeth each side of the ligamental 
spoon. 
Length 20, height 12.5 mill. 
(Semt-fossil in the clays at Portland.) Arctic Seas. 
6. L. THRACI@FORMIS, Storer. Fig. 504. 
(Nucula.) Bost. Journ. Nat. Hist., ii. 122. 
Nucula navicularis, Couthouy, Bost. Journ., ii. 178, t. 4, f 4 (young). 
Shell subquadrate, rounded in front, truncately rounded behind ; 
beaks anterior, with a slight elevation or rib proceeding to basal 
posterior margin; epidermis dusky-green, lighter posteriorly ; 
hinge with 12 teeth each side of the spoon-shaped cavity. 
t=] 
Length 70, height 40 mill. 
New England? Arctic. (From fishes.) 
