184 AMERICAN MARINE CONCHOLOGY. 



3. L. MYALIS, Couthouy. Fig. 499. 



(Nucula.) Bost. Journ. Nat. Hist., ii. 61, t. 3, f. 7. 1838. 

 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 

 colored than L. limatula ; it also differs in the position of the 

 beaks and number of teeth. 



4. L. OBESA, 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.) MassacJiusetts Bay. 



Closely allied to Yoldia pygmsea, Miinst., but that shell is more 

 pointed and upturned at the posterior end. 



5. L. ARCTICA, Gray. Figs. 502, 503. 



Nucula glacialis, Gray, Wood Index Test. Suppl., t. 2, f. 6. 

 Nucula truncate, Brown, Brit. Conch. 84, t. 33, f. 18. 

 Nucula Portlandica, 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. 



(Semi-fossil in the clays at Portland.) Arctic Seas. 



6. L. THRACI^EFORMIS, Storer. Fig. 504. 



(Nucula.) Bost. Journ. Nat. Hist., ii. 122. 

 Nucula namcularis, 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. 

 Length 70, height 40 mill. 



New England? Arctic. (From fishes.) 



