39 



. Fam. MYTILIDJE, Gen. STALAGMIUM, (Nohia.) 



Generic character.. An obuvate, equivalve, marine bivalve, 

 with the hinge margin crenulated, and an oblique, linear, cardi- 

 nal fosset for the cartilage: two rather elongated lateral mus- 

 cular impressions ; palleal impression entire ; nacre perlaceous. 



Obs. I know of but two species of this genus, one of which 

 is minute, and is an abundant fossil in the arenaceous stratum 

 of Claiborne, Alabama. The other is a larger species, recent 

 upon the coast of Rhode Island. 



STALAGMIUM. 



S. maryarataceum. Shell very small, obovate, convex, with 

 distinct radiating striae ; beaks prominent and curved forward ; 

 lunule short, cordate, slightly impressed; inner margin minutely 

 crenulated. 



Locality. Claiborne, Alabama. 



AVICULA. 



A. limula. Shell convex, with slight concentric undulations ; 

 umbo tapering gradually towards the apex, which is acute, 

 but not prominent; wings large and very oblique ; sinus of the 

 posterior margin not profound ; nacre vevy pearl}' and irrides- 

 cent. Height, 1 inches. 



.PECTUNCULUS. 



P. idonens. Shell suborbicular, thick, convex ; oblique, with ra- 

 ther obscure radiating stria?, and minute, intervening lines ; urn- 

 bo convex ; beaks distant, rather prominent and pointed ; cardi- 

 nal teeth large ; truncated in the centre by a rectilinear line ; 

 cavity capacious ; margin crenate. Length \\ in. 



P. aviculoides. Shell suboval, very oblique, with minute ra- 

 diating lines interrupted by regular, prominent concentric stria? ; 

 umbo prominent': beaks rather elevated ; apex acute; series of 

 cardinal teeth interrupted in the centre, by a triangular fosset ; 

 cavity capacious, margin crenulated. Length ^ of an inch. 



P. declivis. Shell ovate acute, rather compressed, with fine 

 concentric crowded lines, and very minute and obscure radiating 

 lines, which become very distinct on the posterior side, near the 

 extremity ; posterior side cuneiform ; beaks small, pointed and 

 recurved ; series of cardinal teeth interrupted under the beaks ; 

 margin entire. Length | of an inch. 



P. tlecisus. Shell longitudinally suboval, equilateral, with ob- 

 solete radiating striae ; posterior end obliquely truncated, umbo- 

 nial slope angulatetf, incurved ; beaks small, pointed and re : 



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