MARINE MOLLUSCA OF THE UNITED STATES. 189 



2. C. FABA, Fabricius. Fig. 516. 



Ulytilus.) Fauna Grcenl. 1780. 



Modiola xiectirmla, Gould, Invert. Mass., 1st edit. 127, t. 85. 



Sliell obovate, A-entricose, with about forty equal radiating 



ribs ; beaks prominent, projecting as far as the anterior margin; 



margin crenulated within ; epidermis brownish-yellow. 



Length n.5, breadth 12.5 mill. 



Arctic Seas to Greenland. 



h. Sides of the shell with radiating lines, middle portion smooth. 

 S. G. MODioLARiA, Gra}'. 



3. C. NIGRA, King. Figs. 517, 518, 519. 



Ann. Nat. Hist., xviii. 239. 

 Mytilus discrepans (?) Mont., Test. Brit. Suppl., 65, t. 20, f. 4. 

 Modiola nexa, Gould, Invert. Mass., 1st edit. 128, f. 8G 



Sliell ovate ; beaks prominent, and placed considerably behind 



the anterior extremity ; epidermis rusty-brown. 



Lengtli 2.5, breadth 1.5 inches. 



Massachusetts., northioards. 



The young shell (Fig. 518), represents if. nexa., Gould. 



4. C. DiscoRS, Linnfieus. Figs. 520, 521. 



{Mytilus.) Syst. Nat., edit. xii. 1159. 1767. 

 Mytilus discrepans, Mont., Test. Brit., 169. 1803. 

 Modiola laivigata, Gray, App. Parry's 2d Voyage, 245. 1824. 



Sliell suboval, broadest behind; beaks nearl3' terminal ; hinder 



extremity somewhat lobed ; anterior ribs about eight; posterior 



ones numerous; greenish-j'ellow, with clouds of olive, becoming 



nearl}' black in old specimens. 



Length 37, breadth 20 mill. 



Massachusetts., noriJncards. {Eur. ) 



The smaller figure represents discors (not.fullj- grown), and the 

 large figure is from an adult specimen (Gray's laevigata). 



5. C. CORRUGATA, Stimpsou. Fig. 522. 



iMytilus.) Shells N. E., 12. 1851. 

 Modiola discors, Gould, Invert. Mass.j 130, f. 84 (not of English authors.) 

 Shell oval, tumid; upper edge somewhat compressed and arch- 

 ing; posterior tip somewhat produced and pointed ; beaks large, 

 nearly terminal ; surface with aboiit sixteen ribs at the anterior 

 third, and very numerous ones at the posterior third; three or 

 four teeth before the beaks; epidermis greenish-3-ellow. 



Massachusetts, northwards. 



