PLATE XXI 



PAGE 



Figs. 1, 2. ATHYBIS SPIRIFEROIDES (Eaton) 211 



1. Ventral valve. 



2. Interior of same, showing the muscular markings. 



Romney formation, Hamilton member, Evitts Creek. 



Figs. 3, 4. MERISTELLA (?) sp 213 



3. Ventral valve. X 6. 



4. Dorsal valve (?). X 6. 



Romney formation, Hamilton member, Iron Bridge over Town 

 Creek, northeast of Oldtown (?). 



Figs. 5-7. PHTHONIA SECTIFROXS (Conrad) 214 



5. External impression anterior end of left valve. Romney formation, 



Hamilton member, Williams Road near church, 3% miles south- 

 east of Cumberland. 



6. A large left valve narrowed by compression. 



7. A large right valve, showing the form and surface characters. 



Hamilton formation, New York. 



Figs. 8-10. PROTHYRIS LANCEOLATA Hall 215 



8. Right valve. X 1%. Romney formation, Hamilton member. Right 



bank of Potomac, about 3 miles below Cumberland. 

 9, 10. Right and left valves. Hamilton formation, New York. 



Figs. 11-13. ORTHOXOTA UNDULATA Conrad 216 



11. View of broken specimen, showing anterior portion of both valves. 



B. & O. R. R. cut, opposite Hancock. 



12. Right valve. McCoys Ferry. 



Romney formation, Hamilton member. 



13. A specimen of medium size preserving both valves. Hamilton 



formation, New York. 



104 



