PLATE LVII 



PAGE 



Figs. 1-3. LINGULA NICKLESI Bassler n. sp 232 



I, 2. Two examples, one partly exfoliated. 



3. View of specimen shown in Fig. 1. X 4. 



Ordovician (Cincinnatian), Maysville group, Fairview forma- 

 tion, Cincinnati, Ohio. 



Figs. 4-7. PLECTORTHIS PLICATELLA (Hall) 241 



4, 5. Front and interior. 



6, 7. Cardinal and profile views of shell. 



Ordovician (Cincinnatian), Maysville group, Fairview forma- 

 tion, Cincinnati, Ohio. 



Fig. 8. RAFINESQUINA ALTEBNATA (Emmons) 265 



Pedicle valve of the usual Maysville form of the species. 



Ordovician (Cincinnatian), Maysville group, Cincinnati, Ohio. 



Figs. 9-12. OBTHOBHYNCHULA LINNEYI (James) 271 



9, 10. Dorsal and ventral views of an average specimen. 



II. Central portion of cardinal region showing distinct cardinal area 



and open delthyrium. X 3. 

 12. Profile views of shell natural size. 



Ordovician (Cincinnatian), Maysville group, Nashville, Ten- 

 nessee. 



Figs. 13-16. ZYGOSPIBA MODESTA Hall 274 



Dorsal, ventral, edge, and side views of an example of this abundant 

 brachiopod. 

 Ordovician (Cincinnatian), Maysville group, Cincinnati, Ohio. . 



Figs. 17-23. ZYGOSPIBA EBBATICA Hall 275 



17. A small example. 



18. Profile view of moderately convex specimen. 



19. Front view of another specimen. 



20. 21. Opposite sides of cast of a large example. 

 22. Cardinal view of large specimen. 



Ordovician (Cincinnatian), Pulaski shales of New York. 



Fig. 24. PTEBINEA DEMISA (Conrad) 284 



Left valve, natural size. 



Ordovician (Cincinnatian), Maysville group, Cincinnati, Ohio. 



Fig. 25. MODIOLODON TBUNCATUS (Hall) 288 



Left side of a cast of the interior, showing usual aspect of the species. 

 Ordovician (Cincinnatian), Maysville group, McMillan for- 

 mation, Cincinnati, Ohio. 



Fig. 26. BYSSONYCHIA BADIATA (Hall) 282 



Left valve of the usual size. 



Ordovician (Cincinnatian), Maysville group, Fairview for- 

 mation, Cincinnati, Ohio. 



Fig. 27. ALLONYCHIA OVATA Ulrich 284 



Left valve, natural size. 



Ordovician (Cincinnatian), Maysville group, Fairview forma- 

 tion, Covington, Kentucky. 



Figs. 28, 29. BYSSONYCHIA PBAECUBSA Ulrich 283 



28. Cast of interior of right valve. 



29. Anterior view of shell showing the byssal opening. 



Ordovician (Cincinnatian), Lorraine shales, Lorraine, New 

 York. 



Figs. 4-8, 13-16 after Meek; 17-23 after Hall; 9-12 after Hall 

 and Clarke; 24, 26 after Hall and Whitfield; and 25, 27-29 after 

 Ulrich. 



407 



