MOLLUSCA. 401 



"Strong and very deep, 12 mm. in the type specimen. Hinge char- 

 acters not observed. 



Remarks. — This is the largest species of the genus, and is rep- 

 resented in the New Jersey collection by a single individual from 

 the Tinton beds, in which the beaks are somewhat more obtuse 

 and the valves more ventricose than in the type of the species 

 in the collection of the Philadelphia Academy of Science. The 

 ■specimen, however, does not differ essentially from other 

 southern examples of the species in the collection oif the National 

 Museum at Washington. The species is characterized by its 

 •great size and its strongly ventricose valves. In the absence of 

 an angular umbonal ridge the species resembles C. antrosa, but it 

 is more oblique than that species, and is much larger than any 

 ■specimen of C. antrosa that has been observed. 



Formation and locality .^T:mion beds;. Beers Hill cut, south 

 of Keyport (129^). 



Geographic distribution. — New Jersey, Georgia. 



Genus Trigonarca Conrad. 



Trigonarca cliffwoodensis n. sp. 



Plate XXX., Fig. 17. 



Description. — Shell subtrapezoidal in outline, the dimensions 

 •of a large individual being: length, 31 mm.; height, 23 mm.; 

 ■convexity of one valve, 7 mm. Anterior margin broadly rounded, 

 the most anterior point at about the mid-height of the shell, pass- 

 ing below with regular curvature into the basal margin; basal 

 margin convex throughout, but becoming straighter posteriorly ; 

 postero-basal margin broadly rounded; posterior margin sub- 

 truncate above. Valves moderately convex, the beaks at about 

 the middle of the hinge-line and but slightly elevated above it; 

 the umbonal ridge rounded, the post-umbonal slope gentle. In- 

 dentation of both an anterior and a posterior muscular ridge 

 present in the casts, both oi them slight but the posterior one 

 ■somewhat the stronger. The larger casts marked by more or 

 less indistinct radiating costse above the pallial impression. Hinge 

 leeth short, arranged in an arcuate line, diverging from either 



26 PAIv 



