LAMELLIBRANOHIATA FEOM THE LOWER LAYERS OP THE UPPER 



MARL BEDS OF NEW JERSEY. 



OSTREID^. 



Genus OSTREA LinnsBus. 



Ostrea glandiformis, n. sp. 



Plate XXVII, Figs. 1-5. 



Shell small, uniform, lower valve proportionally deep, sometimes pro- 

 foundly so, and the upper one ilat or convex, seldom concave. Cardi- 

 nal area narrow, but of considerable length and divided by a distinct con- 

 cave ligamental pit which occupies about one-third of the width in each 

 valve; muscular imprints small and usually inconspicuous. Surface of the 

 shell marked by concentric ridges of growth of greater or less strength, 

 but seldom presenting free lamellose edges, . Very faint indications of radi- 

 ating plicae are sometimes visible on the lower valve, but never to a degree 

 sufficiently marked to be called plicated. Inner margins of the valves not 

 crenulate. 



The species is usually represented only by the internal casts of the 

 cavity of the shell, in which condition they are small, nearly planocon- 

 vex, elongated ovate bodies, having the left postero-lateral margin bent 

 upward and are somewhat bean-like in form. The upper side of the cast 

 is usually depressed convex over the central area, and the margins usually 

 bent upward, while the lower side is gibbously convex and irregular, pre- 

 senting a rather humped appearance. 



There are a number of described species which present some resem- 

 blance to this one, but none sufficiently similar to be considered as spe- 

 cifically identical ; 0, congesta Conrad is perhaps as near as any, but that 

 one is almost invariably fixed to foreign bodies, while this has been 



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