MOLLUSCA. 643 



fords Corner (126^); Navesink marl, near Walnford (148^); 

 Red Bank sand, Red Bank (116), near Middletown (112). 



Geographic distribution. — New Jersey, Mississippi, Texas, 

 Arkansas. 



Corbula cliffwoodensis n. sp. 



Plate LXXII., Pigs. 29-30. 



Description. — The dimensions of an internal cast of a right 

 -valve are: length, 9.5 mm.; height, 8 mm.; convexity, 3.5 mm. 

 Shell subtriangular in outline; the beak large and broad, in- 

 curved. Hinge-line arcuate; antero-cardinal margin sloping 

 abruptly downward to below the middle of the valve; anterior 

 margin rounding from the anterior extremity of the hinge-line 

 into the basal margin; basal margin convex; postero-basal ex- 

 tremity sharply rounded; post-cardinal margin concave. Right 

 valve strongly ventricose in the middle, rounding abruptly to the 

 .anterior and antero-cardinal margin, with an angular umbonal 

 ridge extending obliquely backward from behind the beak in a 

 ■concavely curved line to the postero-basal extremity; post- 

 umbonal slope abrupt, concave; the valve compressed towards 

 the posterior extremity. Surface of the right valve marked by 

 strong, rounded, concentric ribs, which originate at the antero- 

 cardinal margin, grow stronger in the middle of the shell and 

 become obsolete just before reaching the umbonal ridge; about 

 26 of these ribs are recognizable on a shell 8 mm. in height, which 

 regularly increase in strength from the umbo to the ventral 

 margin; post-umbonal slope marked only by concentric lines of 

 growth. . 



Remarks. — Only the right valve of this species has been ob- 

 served. It is a close ally of C. crassiplica, but grows much 

 larger, with comparatively finer concentric ribs, and it lacks the 

 distinct sulcus in front of the umbonal ridge. The species is a 

 close analog of C. bicarinata Con. from the Eocene of Mississippi, 

 having about the same relation to that species that C. crassiplica 

 has to C. murchisoni Lea. The specimens observed are all inter- 

 nal casts and impressions of the exterior. 



Formation and locality. — Cliffwood clay, Cliffwood Point 



<i8s). 



Geographic distribution. — New Jersey. 



