680 SYSTEMATIC PALEONTOLOGY 



Description. " Subtriangular, subequilateral, convex; end margins 

 acutely rounded; umbo slightly prominent; lunule lanceolate, slightly 

 defined by an impressed line; ventral margin rounded." Conrad, 1870. 



Type Locality. Haddonfield, New Jersey. 



" Shell below medium size, the dimensions of an average example are : 

 Height 16.5 mm., approximate length 23 mm., convexity of one valve 

 5 mm.; somewhat triangularly subelliptical in outline. Valves moder- 

 ately convex, beaks small, situated anterior to the middle ; antero-cardinal 

 margin concave ; anterior margin rather sharply rounded above, curving 

 more- gently below and passing without interruption into the broadly 

 rounded ventral margin; posterior margin rather short, obscurely sub- 

 truncate; post-cardinal margin long, gently convex, meeting the antero- 

 cardinal margin at the beak in an angle of 120. Postero-cardinal mar- 

 gin somewhat inflected, especially towards the beak; antero-cardinal 

 margin inflected in front of the beak to form a shallow lunule of moderate 

 width. Surface of shell marked by more or less irregular, concentric 

 lines of growth only. Hinge of the left valve with three cardinal teeth 

 diverging from beneath the beak, the two anterior ones of about equal 

 length, extending directly beneath the beak with a triangular pit between 

 them, the posterior one much more oblique and more elongate. In front 

 of the cardinal teeth is a single low lateral beneath the lunule and parallel 

 with the shell margin. In the right valve there are two divergent, bifid 

 cardinal teeth with a pit beneath the lunule for the reception of the ante- 

 rior lateral tooth of the oposite valve." Weller, 1907. 



The only evidence of the former presence of this species in Maryland 

 and Delaware is a single imperfect cast from the Chesapeake and Dela- 

 ware Canal. 



Occurrence. MATAWAN FOKMATIOX. Summit Bridge, Chesapeake 

 and Delaware Canal, Delaware. 



Collections. Maryland Geological Survey, Philadelphia Academy of 

 Natural Sciences, New Jersey Geological Survey. 



Outside Distribution. Matawan Formation. Woodbury clay, Mar- 

 shalltown clay marl, New Jersey. 



