PLATE XXIX 



PAGE 



Figs. 1-4. PTERINEA FLABELLUM (Conrad) 250 



1. Left valve, showing alternation in size of radiating ribs. Evitts 



Creek. 



2. Internal impression of left valve, showing muscular scar and 



striated ligamental area. Iron Bridge over Town Creek, north- 

 east of Oldtown. 



3. Internal impression of left valve, broken toward the front; but 



showing well the striated ligamental area. Flintstone Creek in 

 Gilpin. 



4. Right valve, partly exfoliated. Evitts Creek. 



Romney formation, Hamilton member. 



Fig. 5. PTERIXEA sp. undet 251 



Left valve showing surface ornamentation. Romney formation, Onon- 

 daga member, Little Moccasin Gap, Va. (After Kindle.) 



Fig. 6. LIOPTERIA L^VIS Hall 253 



Left valve. X 2. Romney formation, Onondaga member, three miles 

 east of Cumberland. (After Kindle.) 



Figs. 7-10. LEPTODESMA ROGERSI Hall 254 



7, 8. External impression X 2 and squeeze of left valve. Romney 



formation, Hamilton member, Evitts Creek. 

 9. Block showing two right valves. X 2. 

 10. Left valve. 



Hamilton formation, New York. 



Figs. 11-13. MYTILARCA (PLETHOMYTILUS) OVIFORJIIS (Conrad) 255 



11. An imperfect right valve. 21st Bridge. 



12. Another imperfect right valve. Evitts Creek. 



Romney formation, Hamilton member. 



13. Left valve of a young shell of elongate form. Hamilton formation, 



New York. 



112 



