MARINE MOLLUSCA OF THE UNITED STATES. 189 
2. C. FABA, Fabricius. Fig. 516. 
(Mytilus.) Fauna Greenl. 1780. 
Modiola pectinula, Gould, Invert. Mass., 1st edit. 127, t. 85. 
Shell obovate, ventricose, with about forty equal radiating 
ribs ; beaks prominent, projecting as far as the anterior margin ; 
margin crenulated within; epidermis brownish-yellow. 
Length 17.5, breadth 12.5 mill. 
Arctic Seas to Greenland. 
b. Sides of the shell with radiating lines, middle portion smooth. 
S. G. MODIOLARIA, Gray. 
3. C. niaRA, King. Figs. 517, 518, 519. 
Ann. Nat. Hist., xviii. 239. 
Mytilus discrepans (?) Mont., Test. Brit. Suppl., 65, t. 26, f. 4. 
Modiola nexa, Gould, Invert. Mass., Ist edit. 128, f. 86 
Shell ovate; beaks prominent, and placed considerably behind 
the anterior extremity ; epidermis rusty-brown. 
Length 2.5, breadth 1.5 inches. 
Massachusetts, northwards. 
The young shell (Fig. 518), represents I. nexa, Gould. 
4. C. piscors, Linneus. Figs. 520, 521. 
(Mytilus.) Syst. Nat., edit. xii. 1159. 1767. 
Mytilus discrepans, Mont., Test. Brit., 169. 1803. 
Modiola levigata, Gray, App. Parry’s 2d Voyage, 245. 1824. 
Shell suboval, broadest behind; beaks nearly terminal; hinder 
extremity somewhat lobed; anterior ribs about eight; posterior 
ones numerous; greenish-yellow, with clouds of olive, becoming 
pearly black in old specimens. 
Length 37, breadth 20 mill. 
Massachusetis, northwards. (EHur.) 
The smaller figure represents discors (not fully grown), and the 
large figure is from an adult specimen (Gray’s lexvigata). 
5. C. cORRUGATA, Stimpson. Fig. 522. 
(Mytilus.) Shells N. E., 12. 1851. 
Modiola discors, Gould, Invert. Mass., 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 about sixteen ribs at the anterior 
third, and very numerous ones at the posterior third; three or 
four teeth before the beaks; epidermis greenish-yellow. 
Massachusetts, northwards. 
