PLATE XX 



PAGE 



Figs. 1, 2. AMBOCCELIA UMBOXATA Conrad 200 



1. Partly exfoliated ventral valve. X 2. Ernstville. 



2. Partly exfoliated dorsal valve. X l 1 /^. Evitts Creek. 



Romney formation, Hamilton member. 

 Figs. 3-6. AMBOCCELIA VIRGINIAN A Prosser n. sp 202 



3. Ventral valve. X 6. 3 miles south of Green Spring, W. Va. Mar- 



cellus limestone. 



4. Ventral valve. X 5. Right bank of Potomac, iy z miles below Cum- 



berland. 



5. Dorsal valve of same specimen. X 5. 



6. Cardinal area and dorsal valve of same specimen, x 5. 



Romney formation, Hamilton member. 

 Figs. 7, 8. AMBOCCELIA PR.EUMBONA Hall (?) 204 



7. Partly exfoliated ventral valve. X 1%. 



8. Interior of ventral valve. X 1^4. Ernstville. 



Romney formation, Hamilton member. 



Figs. 9-11. AMBOCCELIA PR^EUMBONA Hall 204 



9. Ventral valve. 



10. Dorsal valve. 



11. Profile view. 



Hamilton formation, New York. 

 Figs. 12-15. NUCLEOSPIRA CONCINNA Hall 206 



12. Interior of ventral valve (?). X IVz- 



13. Interior of ventral valve. X l ] /&. 



Romney formation, Hamilton member, Ernstville. 



14. Ventral valve. 



15. A portion of surface enlarged, showing the character of the spin- 



ules. 



Hamilton formation, New York. 

 Figs. 16-23. AXOPLOTHECA (CcELospiRA) AcuTiPLiCATA (Conrad) 207 



16. Ventral valve. X 1%. Williams Road near church, 3% miles 



southeast of Cumberland. 



17. Squeeze of same, showing appearance of ventral valve. X I 1 /!. 



18. Dorsal valve. X 1%. Williams Road near church, 3% miles 



southeast of Cumberland. 



19. Squeeze of same, showing appearance of dorsal valve. X I 1 /*. 



20. Interior of partly exfoliated dorsal valve. X l 1 ^- Williams Road, 



S 1 /^ miles southeast of Cumberland. 



21. Squeeze of same, showing appearance of dorsal valve. X I 1 /!. 



22. Squeeze of internal impression of dorsal valve, showing hinge- 



plate, deep dental sockets and median ridge. X 1%. Williams 

 Road near church, 3% miles southeast of Cumberland. 



23. Cast of a dorsal valve. X 2. East of Cumberland. 



Romney formation, Onondaga member. (Fig. 23 after Kindle.) 



Fig. 24. ANOPLOTHECA CAMILLA (Hall) 209 



View of pedicle valve. Romney formation, Onondaga member, Blair 



County, Penna. (After Kindle.) 

 Figs. 25, 26. VITULINA PUSTULOSA Hall 210 



25. Exfoliated ventral valve. X 1%. National Road, northeast of 



Cumberland. 



26. Enlargement from an impression of the surface, showing the ap- 



pearance of the pustules. X 4. 

 Romney formation, Hamilton member. 



103 



