PLATE XXVIII 



PAGE 



Figs. 1, 2. TANCKEDIOPSIS CLARKEI Prosser n. sp 245 



1. External impression of right valve. X 1}4. 



2. Squeeze of same specimen, showing external appearance of right 



valve. X 1&. 



Romney formation, Hamilton member, Western Maryland. 



Figs. 3, 4. LEDA DIVEKSA Hall 247 



3. Right valve. X 2. Romney formation, Hamilton member, McCoys 



Ferry. 



4. Left valve. X 2. Hamilton formation, New York. 



Figs. 5-7. LEDA ROSTELLATA (Conrad) 247 



5. Right valve of young specimen. X 3. Romney formation, Hamil- 



ton member, National Road west of Tonoloway Ridge. 



6. 7. Right and left valves. X 2. Hamilton formation, New York. 



Figs. 8-12. PARALLELODON HAMILTONIJE (Hall) 248 



8. External impression showing part of both valves. 



9, 10. Right and left valves, margins partly broken away. 



Romney formation, Hamilton member, Evitts Creek. 



11. Right valve showing surface markings. Hamilton formation, New 



York. 



12. Left valve of an unusually large individual from near Cumberland. 



(After Hall.) 



Fig. 13. LIOPTERIA CF. CONRADI Hall 252 



Partly exfoliated left valve. Romney formation, Hamilton member, 

 Iron bridge over Town Creek, northeast of Oldtown. 



Fig. 14. LIOPTERIA CONRADI Hall 252 



A large left valve. Hamilton formation, New York. 



m 



