488 CRETACEOUS PALEONTOLOGY. 



foramen being sharp, no hinge-teeth or cardinal area e/cisting. 

 The interior of the valve is strongly marked by moderaely fine 

 striae or ribs, which are flattened on their surfaces ; musclar im- 

 prints not observable. Upper valve very ventricose and srongly 

 arcuate, the beak thin and sharply incurved. Hinge opekas in 

 the lower valve, the cardinal angles spread outward in the brm 

 of auriculations to meet those of the opposite valve. The sdes 

 of the valve are sharply bent inward on a line from the beaito 

 the point of greatest width, forming a hiatus on each side betw^^n 

 the body of the valve and the auriculation, as in the genus Janij, 

 Surface of the valve marked by strong, closely compact, radiatiir 

 ribs ; every fifth or sixth one of which is stronger than the other, 

 and bears short, sharp, curved spines, some of which are nearl}^ 

 one-fourth of an inch long, while the others are only rugose fronii 

 the concentric lamella which cross them. On the depressed spaces \ 

 on the sides of the valve there are no radii, the concentric lines \ 

 only being present. Substance of the shell thin in the cardinal 

 portions and much thickened toward the front. Interior of the 

 valve marked by the radii, and the thickened front margin 

 strongly crenulate." (Whitfield.) 



Remarks. — This species is a rare form restricted to the Nave- 

 sink fauna, the lower valves usually being attached to the interior 

 surface of the shells of Gryphaea convexcu. At Mullica Hill 

 the casts O'f this species have been observed more commonly 

 than at any other locality. The upper free valve does not always 

 have the larger, spine-bearing ribs so conspicuously developed 

 as in the type of the species illustrated by Whitfield. In some 

 specimens the ribs are of essentially uniform size throughout, and 

 in others the larger ones are only moderately developed. The 

 type specimen seems to be rather exceptional in its conspicuous 

 development of the larger ribs. 



Pormation cmd locality. — Navesink marl, Middletown (113^), 

 near. Holmdel (128^), Mullica Hill (169), Holmdel and Free- 

 hold (Whitfield); Tinton beds, Tinton Falls (no). 



Geographic distribution. — New Jersey. 



