332 NORTH AMERICAN INDEX FOSSILS. ■ 



358. S. tullius Hall. (Fig. 422, e.) Devonic. 

 Small, gibbous, subelliptical. Pedicle valve with high cardinal 



area. Plications rather flattened and low. Whole surface covered 

 with fine, uniform, radiating striae and faint concentric ones. 

 Sinus and fold well defined, extending quite to the beak. 

 Upper Hamilton of New York, Northwest Territory. 



359. S. mesistrialis Hall. (Fig. 423.) Devonic. 

 Large. Cardinal angles rounded or mucronate. Sinus and fold 



broad, rapidly becoming expanded toward the front. Plications 16 





Fig. 423. Spirifer mesistrialis with enlargement of striae (Pal. N. Y. IV.). 



to 20. The whole shell, including sinus and fold, conspicuously 

 marked by fine radiating striae. 



Portage and Chemung of New York. 



360. S. (Delthyris) mesicostalis Hall. (Fig. 424, a.) Devonic. 



Cardinal extremities usually extended. Pedicle valve with small 

 beak, the upper part only being abruptly curved over the moder- 

 ately high cardinal area. Sinus angular with a well defined fold in 

 the bottom. Brachial valve with linear cardinal area and mesial 

 fold marked by a deep groove in the middle. Differs from 5. 

 mucronatus in the duplication of the mesial fold and in the long 

 septum extending from the beak nearly to the front of the muscu- 

 lar impression. 



Ithaca and Chemung of New York. 



