MOLLUSCA. 389 



produced and subangular, posterior margin truncate, meeting 

 the posterior extremity of the hinge-line in an obtuse angle, 

 dorsal margin nearly straight, sloping gently backward from 

 the beak to the posterior hinge extremity. From the beak a 

 subangular umbonal ridge passes obliquely backward to the 

 postero-basal angle, and a broadly-flattened or slightly sinuate 

 area passes downward from the beak to about the middle of 

 the ventral margin. The surface markings and hinge characters 

 not preserved on the type specimen, which is an internal cast. 



Remarks. The type is the only specimen of this species 

 which, has yet been observed. It somewhat resembles N. eufau- 

 lensis, but the beaks are more prominent and the anterior mar- 

 gin is very different, the most anterior extension of the shell 

 being near the hinge-line in N. enfaulensis, while in N. angu- 

 latum it is near the base. The radiating markings of the shell 

 may usually be distinguished upon the casts of N. eufaulensis, 

 which is not the case with this species. 



Formation and locality. Navesink marl, Burlington County 

 (Gabb, Whitfield). 



Geographic distribution. New Jersey. 



Nemodon brevifrons Conrad. 

 Plate XXX., Figs. 12-14. 



1875. Neinondon brevifrons Con., Kerr's Geol. N. Car., App. 



A., p. 4, pi. i, fig. 15. 

 1886. Nemodon brevifrons Whitf., Pal. N. J., vol. I, (Monog. 



U. S. G. S., vol. 9), p. 85, pi. 12, figs. 1-2. 

 1905. Nemodon brevifrons Johns., Proc. Acad. Nat. Sci. Phil. 



(1905), p. 9. 



Description. Shell of moderate size, the dimensions of a very 

 perfect right valve being: length, 23 mm. ; height, 13 mm. ; length 

 of hinge-line, 15 mm.; convexity, 6 mm. Shell subrhomboidal 

 in outline, rather strongly convex. Beaks incurved, the umbo 

 rather broad and prominent, and produced above the hinge-line. 

 Hinge-line straight. Anterior margin meeting the hinge-line in 

 an obtuse angle, broadly and evenly rounded, passing with a 



