318 X'ORTH AMERICAN INDEX FOSSILS. 



k. Plications well developed 341. S. gregarius. 



k. Plications nearly obsolete 332. S. eriensis, 



6j Shell moderately convex with extended hinge line 9. 



9. Proportion of length to breadth as I -3 353. S. august us. 



9. Proportion of length to breadth as 1-2 352. S. aiidactilus. 



326. S. radiatus Sowerby. (Figs. 397, 398.) Siluric. 



Beak of pedicle valve strongly incurved ; cardinal area moder- 

 ately high. Median sinus broad and shallow ; median fold flat- 



Fig. 397. Spirifer radiatus Smith. Western type. (After Hall.) 



X 





Fig. 398. Spirifer radiatus. New York type showing variation (Pal. N. Y., II.). 



tened. No plications present but entire surface covered with fine, 

 uniform, radiating striae. 



Clinton and Niagaran of New York, Tennessee, Kentucky, In- 

 diana, Illinois, Wisconsin, Ontario, New Brunswick. 



Fig. 399. Spirifer eudora. (After Hall.) 



327. S. eudora Hall. (Fig. 399.) Siluric. 



Of moderate size. Valves very gibbous. Hinge line less than 



width of shell below, with rounded extremities. Surface marked 



