220 PALEONTOLOGY OF NEW JEESEY. 



with an indistinct umbonal geniculation of the striae ; basal line convex, with 

 a broad and undefined sinuosity behind the middle of the valve. The ex- 

 tremities seem to have been widely gaping, the valves only being in contact 

 near tlie middle of the basal margin. Surface of the cast marked by broad 

 undulations, indicating similar undulations on the surface of the shell par- 

 allel to the margin of the valves. Hinge features and muscular markings 

 unknown. 



Only very imperfect fragments of internal casts of this species have 

 been seen ; the best of which is that illustrated. The species differs from 

 P. decisa Conrad, which occurs in the lower beds, in the narrower extremi- 

 ties, especially the posterior end, which lacks the broad oblique truncation 

 so characteristic of that species. The beaks are also proportionally larger, 

 and the posterior cardinal line more deeply excavated behind them. 



Formation and locality. — In the dark green sands at the base of the 

 Upper Marls, near New Egypt, New Jersey, and is apparently an uncom- 

 mon species. 



ANATINID^. 



Genus PEEIPLOMYA Conrad. 



Periplomya truncata, n, sp. 

 Plate XXVIII, Figs. 20 and 21. 



Shell of medium size, transversely elliptical in general outline, and pro- 

 portionally ventricose, with subequal valves ; in the cast, the condition under 

 which the species is known, the beak of the right valve appears the largest 

 and most prominent. Beaks full, but of small size, turned toward the pos- 

 terior extremity, and not projecting much beyond the hinge margin, their 

 location being perhaps a little behind the middle of the shell's length. 

 Length of the shell abo^"- twice the height ; anterior end rather sharply 

 rounded and wider t' ,.i the opposite, the anterior cardinal border beino- 

 very slightly arched ; basal line broadly and evenly curved ; posterior end 

 narrowed from behind the beaks, and the posterior cardinal margin concave, 

 abruptly so near the beaks ; posterior extremity truncate. Umbonal ridge 

 angular, the disk of the valve in front of it being full and ventricose, while 



