LAMELLIBEANCHIATA OF THE PLASTIC CLAYS. 27 



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

 mens are both very ventricose, with a somewhat subquadrangular 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, [f I have rightly 

 identified the species there can be no reason for referring it to Artartein 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 GI^ATH0D0:N^. 



Gnathodon? tenuidens, n. sp. 



Plate II, Figs. 7-10. 



Shell of moderate size, very ventricose, very broadly ovate or sub tri- 

 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 w^ith a much 



