122 MR. CONRAD'S DESCRIPTIONS 



P. LiNTEA. PI. 12, fig. 25. — Oblong, compressed, with rather fine, very regular concentric lines closely 

 arranged ; anterior margin acutely rounded, the extremity in a line above the middle of the valve ; 

 posterior side shortest ; hinge line rectilinear, oblique ; posterior side vi^ith acute lines larger and more 

 prominent than those of the middle and anterior side ; umbonial slope subangular. Length 1 \. Rare. 



P. MississippiENSis. PI. 12, fig. 26. — Oblong-ovate, inequilateral, compressed ; disk flattened and with 

 slight concentric lines ; posterior side with lamellaeform lines ; dorsal margin oblique ; posterior 

 end sub-truncated ; umbonial slope undefined ; anterior hinge margin slightly more oblique than the 

 posterior ; end acutely rounded. 



CRASSATELLA. 



C. MISSISSIPPIENSIS. PI. 13, figs. 7, 10. — Ovate-trigonal, inequilateral, thick and ponderous; surface 

 coarsely striated ; summits flattened, sulcated ; umbo plano-convex, with numerous sulci, obsolete 

 behind the umbonial slope, which is angulated and subcarinated above ; posterior extremity truncated, 

 direct; basal margin slightly contracted anterior to the umbonial slope ; inner margin crenulated. 

 Length 3. Common. 



This species is variable in outline, and allied to C tumida of the Paris basin. 



CARDIUM. 



C. EVERSUM. PI. 12, fig. 18. — Ovate, elevated, subequilateral, ventricose, thin, with numerous approximate, 

 slender, rounded ribs, distinctly crenulated anteriorly towards the margins; umbonial slope 

 subangulated ; posterior extremity subtruncated, direct ; summit very prominent ; ribs crenulated on 

 the sides in the middle of the valves, or finely aculeated. Height 1 2-10. Length not quite as much. 

 Rare. 



C. GLEBosuM. — Ovate, ventricose, with numerous flat ribs, slightly carinated on the margins and numerous 

 approximate, prominent arched scales. Height \\. 



Rare, and obtained only in fragments. 



C. DivERSUM. PI. 13, fig. 8. — Trigonal, ventricose, subequilateral, thin, with concentric lines and more 

 approximate fine but obtuse radiating lines ; umbonial slope rounded, and the posterior space from the 

 umbonial slope with profound radiating strise ; posterior side slightly waved or contracted ; summits 

 very prominent ; basal margin rounded in the middle, contracted posteriorly ; posterior extremity 

 subtruncated; inner margin densely crenate. Height 1 2-10. Length 1 3-10. Abundant. 



Allied to C. Nicolleti, nob. When viewed through a magnifier, the interstices of 

 the concentric lines have a singular imbricated appearance. 



C. vicKSBURGENSE. PI. 12, fig. 16. — Cordate, ventricose, with about twenty-four ribs; angular and 

 profound ; towards the anterior margin obsolete ; summit prominent ; nearest the anterior end ; anterior 

 margin nearly straight and direct; posterior end subtruncated. Height 3-10. Length 4-10 nearly. 

 Rare. 



TELLINA. 



T. PECTOROSA. PI. 12, fig, 27. — Subtriangular, elevated, smooth and polished, ventricose, beaks medial; 

 anterior end obtuse, rounded ; posterior side somewhat cuneiform, with a slight wave or fold ; basal 

 margin profoundly rounded. Length 6-10. Height 5-10. 



