82 PALAEONTOLOGY OF NEW JERSEY. 



interspaces. The lower or basal portion is marked by very strong concen- 

 tric striae parallel to the margin, so ver}- irregular as to often form strong 

 undulations of the surface. Line of division between the upper and lower 

 sections of the valves very strongly marked on the cast, often presenting 

 the appearance of a distinct suture. Posterior margin of the shell appar- 

 ently double, being deeply emarginate or lobed at the line of division 

 between the upper and lower portions of the valve. The margin of the 

 upper division is obliquely truncate, receding from below to the hinge-line, 

 and strongly curved inward at the central emargination. Lower section 

 also strongly lobed and somewhat rounded. 



All the specimens seen are quite imperfect, and are more or less casts 

 of the interior. The strong line of division between the upper and lower 

 sections of the valve gives one the impression of a double shell, or of two 

 distinct shells united along the margins; and were it not for the surface 

 markings the}' would greatly resemble in form that of a large Conularia. 

 This species is very closeh' allied in form and surface markings to P. 

 quadfangularis Goldf (Petref, p. 157, vol. ii, pi. 127, fig. 7), from the Cre- 

 taceous sandstones of Westphalia and Saxony, and in the Academy of Nat- 

 ural Sciences collection is so marked by L Lea, Esq., on the label; but it 

 differs very materially in its much greater degree of e.xpansion toward the 

 front of the shell. 



Formation and localify — One large individual cast is from the coarse 

 marls at Burlington, N. J., and there are several imperfect specimens, par- 

 tially retaining the shell, from the fine micaceous clay below the Lower 

 Marls at Haddonfield, New Jersey. 



Suborder UIMYARIA. 



ARCID^. 



Genus ARCA Linn. 



Area altirostris. 



Plate XII, Fig.s. 2a and 23. 



Area altirostris Gabb. Proc. A. N. Sci., Phil., 1861, p. 325. Synopsis, p. — . Meek, 

 Clicck-list, p. — . Geol. Siirv. N. J., 1868, p. 725. 



Shell small, transverse in the cast, wath very much elevated and dis- 

 tant beaks, which are situated a little nearset to the anterior end. Valves- 



