LAMELLIBEANCHIATA OP THE LOWER MARLS. 177 



Formation and locality. — In the micaceous clays below the Lower Marl 

 Bed, at the Rev. G. C. Schank's pits, near Marlborough, Monmouth County, 



New Jersey. 



Genus PERIPLOMYA Conrad. 



Am. Jour. Conch., Vol. VI, p. 76 = Leptomya Gou., Am. Jour. Conch., Vol. Ill, p. 15. 



Periplomya elliptica. 



Plate XXIII, Figs. 14 and 15. 



Anatina elliptica Gabb. P. A. K. S., Phil., 1861, p. 321. Meek, Check-list, p. 15. Geol. 



Surv. N. J., 1868, p. 727. 

 Periplomya elliptica Gabb. P. A. N. S., Phil., 1876, p. 305. 



Shell small, inequivalve, and very inequilateral, subovate in outline, 

 largest across the anterior side of the beaks, and strongly constricted just be- 

 hind them, the posterior end being narrowed on the hinge-line and excavated 

 at this point. Valves somewhat ventricose, the right one less convex than 

 the left, and very decidedly depressed in the central region and toward the 

 basal line, showing a decided twist or arcuation of the valves as seen in a 

 basal view. Anterior end broadly rounded, and the posterior pointedly 

 rounded. Beaks small, appressed, incurved, and apparently directed back- 

 ward, as is usual in this group of shells, from the expansion or inflation of 

 the anterior side of the hinge-line. Cardinal margin, as seen on the cast, 

 inflected both in front and behind the beaks, forming an apparent lunule 

 and escutcheon on the cast, probably produced mainly from a thickening 

 of the hinge-plate within. Muscular imprints and palllal line and hinge not 

 observed. 



This appears to be a rare form of shell In the Cretaceous strata of 

 America, only a very few individuals having been observed by any one. 

 I have seen only two individuals besides Mr. Gabb's type, but the latter 

 author speaks of Mr. Conrad having seen three specimens. Tlie generic 

 relations of the species are somewhat obscure, as none but internal casts 

 have been found, which do not retain the features of the hinge. Mr. Con- 

 rad appears to have identified it positively with his genus Periplomya for 

 Mr. Gabb, but I can see no valid reason why it should not be placed under 

 Agassiz's genus Corimya, 1843, a genus which occurs in Europe in tlie Cre- 

 taceous and Jurassic. There certainly seems to be no difference in the form 

 4418 MON 9 12 



