338 Systematic Paleontology 



Occurrence. — Heldekberg Formation, Becraft Member. Ernstville. 

 Oeiskany Formation, Ridgely Member. Cash Valley, Winchester 

 Road near Cumberland, and North Branch, 21st Bridge. Siiriver 

 Member. Williams Eoad near Cumberland, Monster Rock opposite 

 Keyser, West Virginia. 



Collections. — Maryland Geological Survey, U. S. National Museum. 



ClIONETES JERSEYENSIS Wellcr 



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 ijromineut; cardinal area low, with 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 

 front margin. On the younger shells the ribs are usually finer and more 

 angular and the lateral ones often have a slight anterior curvature as they 

 approach the margin. As the shells increase in size this peculiar curva- 

 ture of the ribs becomes more and more conspicuous, and can always be 

 detected to a greater or less degree in the adult individuals, and it is always 

 more conspicuous in the brachial than in the pedicle valve. Just anterior 

 to the beak in both valves there is a small area where the radiating ribs 

 are obsolete. In addition to the radiating ribs, both valves are marked by 

 exceedingly fine, concentric lines. 



" The dimensions of a large individual are : Length 14 mm. and width 

 22 mm." Weller, 1903. 



This species is an exceedingly variable one in form. The larger speci- 

 mens may be recognized by the peculiar curvature of the radiating ribs. 



