MOLLUSCA. 



475 



increased growth. Valves slightly convex. Hinge short, from 

 half toi two-thirds as long as the width of the body, of the shell, 

 strongly and distinctly auriculated. Beaks of the valves small 

 and pointed, and the cardinal slopes long, straight or slightly 

 concave, extending to near the point of greatest width of the 

 body of the shell. Left valve smooth or but faintly marked by 

 fine concentric lines, and a few (five or six) very faint radii. 

 Ears smaller than in the opposite valve, both sloping toward the 

 beak on the outer margin. Right valve marked with crowded 

 concentric foJds or elevated lines; also by five or six radiating 

 lines; not always present. On most specimens there are dis- 

 tinctly rounded concentric folds or varices, but on some they 

 are thin, sharp lines; always more crowded and usually finer 

 toward the front, in adult specimens. Ears very distinct ; that of 

 the posterior side sloping toward the beak and the anterior one 

 rounded at the extremity and deeply notched." (Whitfield.) 



Remarks. — This species is not uncommon in both the Mer- 

 chantville and Woodbury formations. It is especially abundant 

 in the Woodbury at L,orillard, but, like so^ many of the species 

 from that locality, it grows to a much larger size than elsewhere ; 

 the average size of the individuals from there is not far from 15 

 mm. in height, while the largest ones are 17 mm. or more. The 

 types of the species illustrated by Whitfield are 9 and 10 mm. in 

 height, and he states that it seldom exceeds "half an inch in 

 height" (12.5 mm.); the specimens from other localities than 

 Lorillard agree with this statement. As noted by Whitfield, the 

 species is a close ally of Pecten simplicum Con., and the New Jer- 

 sey specimens have frequently been identified with that species. 

 It differs especially from that species, however, in the conspicu- 

 ous concentric markings which are always present upon the left 

 valve at least. The larger specimens of the species from Loril- 

 lard somewhat resemble the young of Pecten hurlingtonensis 

 Gabb, but the concentric bands are narrower and do not con- 

 tinue across the auriculations as in that species. 



Pormation and locality. — Merchantville clay-marl, near Mata- 

 wan (lOi), near Jamesburg (1-39, 141), Merchantville' (162), 

 Lenola (163) ; Woodbury clay, Lorillard (102), near Matawan 



