390 CRETACEOUS PALEONTOLOGY. 



regular curvature into the gently convex ventral margin, postero- 

 ventral margin rather broadly rounded and passing into the 

 obliquely subtruncate posterior margin above, which meets the 

 hinge-line in an obtuse angle. The umbonal ridge prominent, 

 broadly rounded or somewhat inflated, the posterior slope being 

 narrow and somewhat abrupt. Surface of the shell marked by 

 concentric lines of growth, and in some specimens by faint radiat- 

 ing lines, which are more conspicuous upon the anterior portion of 

 the shell. The anterior hinge-teeth are three in number, rather 

 short and slightly curved, but nearly parallel with the hinge-line, 

 the posterior teeth are also three in number, perhaps a little longer 

 than the anterior ones, straight and subparallel with the hinge- 

 line. : V 



Remarks. Johnson states that the specimen of this species 

 described and illustrated by Whitfield as from the Woodbury 

 clay, near Haddonfield, probably did not come from that locality, 

 but from Snow Hill, North Carolina, the type locality for the 

 species. In the recent Survey collections the species has not been 

 recognized in any of the Woodbury clay localities, but it does 

 occur in the Cliffwood clay and the Wenonah sand. In the best 

 specimen observed from the Cliffwood clay the radiating mark- 

 ings of the shell, as shown in an impression of the exterior, are 

 apparently obsolete, the markings being essentially as shown in 

 Conrad's original illustration of the species. One of the speci- 

 mens from, the Wenonah sand, on the other hand, with np essen- 

 tial differences in the contour of the shell, exhibits some faint 

 radiating markings, which are more strongly developed on the 

 anterior portion of the shell, agreeing essentially with Whit- 

 field's description. From the Wenonah sand, near Crawfords 

 Corners, a single specimen of an internal cast has been collected, 

 which agrees closely in general form with the other shells referred 

 to this species, but it is much larger than any other individual 

 observed, being 38 mm. long, and 20 mm. high. It is possible 

 that this specimen should be referred to a distinct species, per- 

 haps undescribed, but in the absence of additional material, 

 especially specimens preserving the external markings, it is 

 thought best to refer it to this species provisionally. The species 



