LAMELLIBEANCHIATA OP THE PLASTIC CLAYS. 27 



very istrong, and a ferruginous replacement of the ligament. The speci- 

 mens are both veiy ventricose, with a somewhat subquadi-angular outline 

 and a moderately angular umbonal ridge. The beaks are small and nearly 

 anterior, hinge line short and oblique, with a small ligament. Anterior end 

 short and rounded, while the posterior is broadly truncated, correspond- 

 ing to the rather broad and abrupt postero-cardinal slope. If I have rightly 

 identified the species there can be no reason for referring it to^r^ar^ein the 

 light afforded by the two specimens, but every appearance would Indicate 

 their relations to the genus Corbicula, with which I have placed it. 



Formation and locality. — Mr. Conrad's specimen was from near Wash- 

 ington, Middlesex County, N. J. One of the two specimens which I have be- 

 fore me came from the top layers of Sayre and Fisher's brick and clay yards 

 near Sayreville, N. J., and the other from near Woodbridge, New Jersey. 



Genus GNATHODON. 



G-nathodon? tenuidens, u. sp. 



Plate II, Figs. 7-10. 



Shell of moderate size, very ventricose, very broadly ovate or subtri- 

 angular, with strong and rather tumid, enrolled beaks, which are directed 

 forward and project considerably beyond the line of the hinge. Posterior 

 hinge border gently arcuate, extending more than two-thirds of the dis- 

 tance from the beak toward the basal margin of the shell. Postero-basal 

 angle sharply rounded, and the basal margin broadly arched; anterior end 

 less sharply and more regularly rounded than the postero-basal. Surface 

 of the shell, as indicated on the partial casts and imprints left in the hard- 

 ened clay, smooth or marked by fine lines of growth only. On the cast of 

 a right valve there are indications of two principal cardinal teeth beneath 

 the beak, and a long, rather slender, lateral tooth. The muscular impres- 

 sions are not visible on the posterior side, but on one specimen the anterior 

 scars seem to have been large and deep ; but this feature is not very 

 satisfactorily determined. 



The shell has had nearly the form of G. cuneata of our Southern Atlantic 

 coast, but has been a much thinner and more delicate shell with a much 



