PLATE LXXV 



PAGE 



Fig. 1. GRAMMYSIA sp 450 



Anterior part of left valve. Helderberg formation, Keyser member, 

 Keyser, W. Va. 



Fig. 2. LEPTODESMA (?) sp 451 



Internal cast of right valve. Oriskany formation, Ridgely member, 

 Rock Enon Spring, W. Va. 



Figs. 3, 4. MYTILARCA MARYLANDICA Ohern n. sp 452 



3. Internal cast of left valve. 



4. Anterior view of internal cast. 



Helderberg formation, Cumberland. 



Figs. 5, 6. MYTILARCA CORUIFORMIS (Hall) 452 



5. Profile view from the anterior side of the shell. 



6. View of the right valve, having the posterior cardinal extension 



abraded. 

 New Scotland formation, New York. 



Fig. 7. MYTILARCA ( PLETHOMYTILUS ) ROWEI Ohern n. sp 453 



Left valve. Oriskany formation, Ridgely member, Hancock. 



Figs. 8-10. AMPHICCELIA TJLRICHI Maynard n. sp 453 



8. Anterior view of internal cast. 



9. Internal cast of right valve. 

 10. Left valve. 



Helderberg formation, Keyser member, Keyser, W. Va 



66 



