LAMELLIBKAISOHIATA OF THE LO^YER MARLS. 65 



the cardinal and basal margins being nearly parallel and the ends nearly 

 equally rounded. Valves ventricose, most gibbous at the anterior end ; 

 beaks inflated but not prominent, nearly but not quite terminal, but placed 

 on a line with the hinge, or nearly so. Hinge extending about two-thirds 

 the length of the shell and rounding into tlie posterior end, which is longer 

 below than above the middle. Surface of the shell polished, but with very 

 strong concentric undulations parallel to the margin. Hinge and features 

 of the interior unknown. Substance of the shell extremely thin. 



I do not think the shell is a true Modiola^ but the specimens examined, 

 two only, are not in a condition to reveal any of the generic features, both 

 being crushed and badly broken, and by far too thin and fragile in substance 

 to possess them in any degree of strength I have referred it back to Modiola 

 Lamarck, not thinking it advisable to replace that name by the pre-Linnean 

 one adopted by Mr. Meek in his list, or Iby the later one of Volsella, 



Formation and locality. — In the micaceous clays of the Lower Green Marls, 

 at Haddonfield, New Jersey. From the collection of the Academy of Nat- 

 ural Sciences, Philadelphia. 



Modiola Burlingtonensis, u. sp. 

 Plate XVII, Figs. 8 and 9. 



Shell of moderately large size, ver}^ ventricose, and with subparallel 

 dorsal and ventral margins, large prominent umbones and incurved beaks 

 situated near the anterior end but not terminal, the anterior margin percept- 

 ibly extending beyond them and rounded. Umbonal ridge prominent and 

 subangular, especially near the beaks, and becoming broader and more 

 rounded posteriorly; surface of the valves strongly constricted and sinuate 

 in front of the ridge and the anterior surface again inflated; cardinal slope 

 comparatively broad and slightly concave toward the postero-cardinal 

 border. Hinge line straight and three-fifths as long as the shell, and rather 

 strongly impressed in the internal cast; postero-cardinal margin rounding 

 rapidly forward from the more narrowly rounded posterior extremity. Sur- 

 face of the cast, the only condition under which it is known, apparently 

 smooth or marked only by irregular concentric lines of growth, some of 

 which produce undulations of considerable strength on the casts. On one 

 4418 MON 9 5 



