LAMELLIBEANCHIATA OF THE LOWER MAELS. 183 



Fonnation and locality. — In the micaceous clays of the Lower Marls at 

 Haddonfield, New Jersey. Borrowed from the collection of the Academy 

 of Natural Sciences of Philadelphia. 



Genus LEPTOSOLEN Conrad. 



(Am. Jour. Conch., vol. iii, p. 15 and p. 188.) 



Leptosolen biplicata. 

 Plate XXV, Figs. 1 and 2. 



Siliquaria biplicata Conrad. J. A. N. S., Phil., 2d sev., Vol. Ill, p. 324, PI. XXXIV, 

 Fig. 17. Gabb, Synop., p. 170. Meek, Siuitb. Inst., Check-list, p. 15. 



Leptosolen biplicata Conrad. Am. Jour. Conch., Vol. Ill, pp. 15, 188. Meek, Geol. Kept. 

 N. Jersey, 1868, p. 727. Gabb, P. A. N. S., 1861, p. 301. 



Shell of medium size, two and a half to three times as long as wide, 

 •with parallel dorsal and basal margins. Valves quite convex when not 

 compressed, and gaping at each extremity; beaks small and inconspicuous, 

 situated within the anterior third of the length ; posterior extremity truncate, 

 a little the longest below the center; anterior end more distinctly rounded, 

 longest above the middle. Surface of the shell marked by concentric lines 

 of growth, which are wiry and distinct upon the impressions in the marls, 

 but indistinct on the internal casts. On the anterior part of the shell there 

 are two indistinct plica extending from in front of the beaks, one to the 

 anterior basal angle and the other to the margin of the valve about midw^ay 

 between the first and the antero-dorsal angle. On the casts there is a strong 

 groove extending obliquely across the valve from the beaks to near the 

 base, gradually widening from its origin and passing gently backward in its 

 extension, marking the position of an internal rib on the shell. The hinge 

 features cannot be determined from either of the two imperfect specimens 

 before me. The larger of the specimens would indicate a shell of nearly 

 two inches in length with a width of almost five-eighths of an inch. 



This species is the type of the genus Leptosolen., the principal generic 

 feature resting upon the single direct tooth of the right valve, a feature 

 which cannot be seen on the internal casts found in this State; and as Con- 

 rad has not figured this feature so far as I can ascertain, I am not able to 

 judge of the validity of the characters. 



