PETRICOLIDiE. 39 



PETKICOLA DACTYLUS. 



Plate VII. Fig. 1. 



Petricola dactylus, Sow., Gen. Shells, pi. 3. 



Petricola dactylus, Say, Amn. Conch., pi. 60, fig. 2. 



Petricola dactylus, Gould, Invert. Mass., p. 65, fig. 41. 



Petricola dactylus, Be Kay, Zool. New- York, Art. Mollusca, p. 228, pi. 28, fig. 283, a, b. 



Petricola dactylus, Ravenel, Cat. Coll. Shells, p. 3. 



Petricola dactylus, L. R. Gibbes, Tuomey's Geol. So. Ca., appendix, p. xxi. 



Petricola dactylus, Stimpson, Shells of New-England, p. 24. 



Petricola dactylus, Adams, Gen. Recent Shells, Vol. 2, p. 441. 



Petricola dactylus, Say's Conch. U. S., (Binney,) p. 222. 



Description. Shell elongately-ovate, thick, irregular, inequilateral, covered with 

 radiating lines, and ribs; those on buccal side raised, distinct, without scales; no areola 

 before the beaks. 



Common along the whole Atlantic coast of North- America. 



Plate VII. Fig. 7. 



Museum, College of Charleston. 



Genus, MACTRA.— Linn. 



MACTRA SIMILIS. 

 Plate VII. Fig. 8. 



Mactra similis, Say, Jour. Acad. Nat. Sci., Vol. 2, p. 309. 



Mactra similis, Be Kay, Zool. New-York, Art. Mollusca, p. 230. 



Mactra similis, Ravenel, Cat. Coll. Shells, p. 2. 



Mactra similis, Stimpson, Shells of New-England, p. 20. 



Mactra similis, L. R. Gibbes, Tuomey's Geol. So. Ca., appendix, p. xxii. 



Mactra similis, Tuomey 4- Holmes, Pleiocene Foss. So. Ca., p. 97, pi. 23, fig. 8. 



Mactra similis, Say's Conch U. S., (Binney,) p. 101. 



Description. Shell oblong-oval, equilateral, surface finely marked with concentric 

 lines of growth, which are almost obsolete, and always interrupted irregularly with two or 



