PLATE X 



PAGE 



Fig. 1. STROPHEODONTA DEMISSA (Conrad) 136 



Ventral valve. Romney formation, Hamilton member, Hancock-Har- 

 risonville Road, about 2 miles north of Hancock. 



Figs. 2-5. STROPHEODONTA (DOUVILLINA) IN^QUISTRIATA (Conrad) 138 



2. Interior of ventral valve, showing fragment of shell near lateral 



margin. 



3. Enlargement of same, showing striae. X 6. 



4. Squeeze of No. 2. 



Romney formation, Hamilton member, Evitts Creek. 



5. Interior of ventral valve. Hamilton formation, New York. 



Figs. 6, 7. STROPHEODONTA CONCAVA Hall 139 



6. Interior of dorsal valve, showing its strongly pustulose character 



and part of crenulated hinge-line. Romney formation, Hamilton 

 member, Evitts Creek. 



7. Ventral valve which is carinate along the center. Hamilton forma- 



tion, New York. 



Figs. 8, 9. PHOLIDOSTROPHIA PENNSYLVANIA Kindle 141 



8. Ventral valve of type. X 3. East of Cumberland. 



9. Interior of ventral valve, showing short and very slender median 



septum. Berkeley Springs, W. Va. 

 Romney formation, Onondaga member. (After Kindle.) 



Figs. 10, 11. LEPT.ENA RHOMBOIDALIS (Wilckens) 141 



10. Fragment of ventral valve. Romney formation, Hamilton member, 



Ernstville. 



11. View of dorsal valve. Hamilton formation, New York. 



