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Figs. 1, 2. CHONOSTROPHIA COMPLANATA (Hall) 341 



1. Exterior of ventral valve. 



2. Internal cast of ventral valve. 



Oriskany formation, New York. 



Fig. 3. CHONOSTROPHIA HELDERBERGI/E Hall and Clarke 342 



Ventral valve. Helderberg formation, New Scotland member, Dawson. 



Figs. 4-7. GYPIDULA (SIEBERELLA) COEYMANENSIS Schuchert n. name 342 



4. Interior of ventral valve. 



5-7. Dorsal, anterior, and side views. 



8. Dorsal view of large individual. 



Coeymans formation, New York. 



Figs. 9-11. GYPIDULA (SIEBEREJXA) COEYMANENSIS VAR. PROGNOSTICS 



Schuchert n. var 344 



9, 10. Ventral and side views of unusually large individual. 

 11. Ventral view of individual of usual size. 



Helderberg formation, Keyser member, Keyser, W. Va. 



Figs. 12-18. GYPIDULA (SIEBERELLA) COEYMANENSIS VAR. CORRIGANENSIS 



Maynard n. var 345 



12-15. Anterior, side, dorsal, and ventral views of a large individual. 



Cumberland. 



16-18. Dorsal, ventral, and side views of type. Devil's Backbone. 

 19. Dorsal view. Keyser, W. Va. 



Helderberg formation, Keyser member. 



Figs. 20-22. GYPIDULA SUBGLOBOSA Maynard n. sp 346 



Ventral, side, and dorsal views. Helderberg formation, Keyser 

 member, Pinto. 



Figs. 23, 24. RHYNCHOTRETA CUMBERLANDIA Rowe n. sp 347 



Dorsal and side view of a large specimen. Oriskany formation, 

 Ridgely member, Cumberland. 



Figs. 25-29. STENOCHISMA FORMOSA Hall 349 



25, 26. Dorsal and ventral views of a large individual. 



Becraft formation, New York. 

 27-28. Side and ventral view of smaller individual. 

 29. Dorsal view of young specimen. 



New Scotland formation, New York. 



