LAMELLIBEANCHIATA OF THE LOWER MARLS. 85 



cave basal line. The posterior end is somewhat narrowed and obliquely trun- 

 cate, the basal angle being prolonged. Anterior end rather more broadly 

 rounded. The surface characters and hinge sti'ucture are yet unknown. 



In its general appearance the cast somewhat resembles N. EiifauUits'is, 

 but the beaks would appear to be ver}' much more prominent and more 

 nearly centrally situated. I strongly suspect this to be the same species 

 more recently described as Trigonarca passu by Mr. Conrad, from a still 

 smaller specimen, from Crosswick's Creek, though I have been unable to 

 find any representative of that species in the collection of the Academy of 

 Natural Sciences at Philadelphia, or elsewhere; and I may be mistaken in 

 my inference. 



Formation and locality. — In the Lower Green Marls in Burlington 

 County, New Jersey. 



Nemodon brevifrons. 



Plate XII, Figs. 1 and 2. 



Nemodon brevifrons CoDracl. Kerr's Geol. Surv. N. Car., Appeudix, p. 4, PI. 1, Fig. 15. 



Shell of moderate size, transversely subovate or subrhomboidal in 

 outline, moderately convex, considerablj^ less than twice as long as high, 

 with moderate-sized beaks for an Area, which are rather within the anterior 

 third of the length, are but little projecting above the line of the hinge, 

 and are closely approximate. Umbonal ridge prominent, strong, and ratlier 

 inflated, leaving a rather narrow and somewhat abrupt posterior slope. 

 Hinge-line a little more than half the length of the shell, and the cardinal 

 area narrow and slightly sinuous. Anterior end of the shell somewhat 

 broadly rounded, nearly evenly so above and below; basal margin broadly 

 curved and the posterior end narrow, almost cuneate below and rapidly 

 sloping above to the extremity of the hinge-line. Surface of the shell 

 marked by fine subobsolete, radiating strige, which form lines of small 

 punctures where they cross the nearly equally fine concentric markings; 

 these are strongest on the anterior and middle parts of the valves and be- 

 come almost obsolete on the posterior slope and on the umbonal ridge. 

 Substance of the shell, very thin. The teeth are three short laterals on the 



