14 The Fauxa of the Keyser Member of the 



the median portion and descending rather abruptly towards the lateral 

 margins. Greatest convexity about 7 mm. anterior to the beak, beak only 

 slightly incurved, prominent, and extending high above the beak of the 

 dorsal valve. 



Dorsal valve plano-convex to depressed convex; beak straight and ex- 

 tending to the hinge-line. A medial sinus extends from the beak to the 

 base, which is narrow at the beak and gradually wider anteriorly and con- 

 tains three or four radiating ribs. A slight emargination is produced 

 where the dorsal sinus meets the ventricose portion of the ventral valve at 

 the base of the shell. Surface of both shells marked by strong radiating 

 simple rounded ribs which extend from the beaks to the base of the shell 

 and increase by implantation and interstitial addition, and are crossed by 

 faint concentric lines of growth. 



This form is not easily confused with any other species. 



Dimensions: Length 16.5 mm.; width 14 mm. 



Occurrence. — Helderberg Formation, Keyser Member, Cumber- 

 land, Maryland; Keyser, West Virginia. 



Collection. — U. S. National Museum. 



Family PRODUCTIDAE 



Genus CHONETES Fischer de Waldheim 



Chonetes jerseyensis Weller 



Plate LXI, Figs. 17-19 



Chonetes jerseyensis Weller, 1900, Ann. Rept. Geol. N. J. for 1899, p. 8. 

 Chonetes jerseyensis Weller, 1903, Geol. Surv. N. J., Pal., vol. iii, p. 230, pi. xx, 

 figs. 11-16. 



Description. — " Shell concavo-convex or nearly plano-convex, length 

 about two-thirds the breadth, hinge-line usually a little shorter than the 

 greatest breadth, lateral and anterior margins regularly rounded. 

 Pedicle valve depressed convex, the greatest convexity near the beak: 

 beak small, not prominent; cardinal area low, Avith as many as seven 

 slightly oblique marginal spines on each side of the beak upon the larger 

 specimens. Brachial valve slightly concave or nearly flat. Both valves 

 marked by rather coarse, radiating ribs, which increase by implantation 

 and bifurcation, three or four of them occupying a space of 2 mm. at the 



