PLATE L 



PAGB 



Figs. 1-5. CONOTRETA HDSTi (Walcott) 234 



1. Internal cast of pedicle valve showing impressions of the strong apical 



callosity and the radiating ridges. X 8. 



2. Apical view of the same. The subtriangular posterior slope and its obscurely 



defined median furrow are visible. X 9. 



3. Cardinal view of a young individual with very faint posterior slope. X 12. 



Ordqvician (Mohawkian). Trenton Is., Trenton Falls, New York. 



4. Cardinal view of very small example retaining the shell. X 25. 



5. Profile of the same. 



Ordovician (Mohawkian) Trenton Is., Covington, Kentucky. 



Figs. 6-8. LINGULA BICINIFORMIS (Hall) 232 



6. Well preserved ventral valve. 



7. Enlarged sketch of the posterior portion of the same specimen showing growth 



stages, p, protegulum ; o, obolella ; s, nealogic. 



Ordovician (Mohawkian) Trenton shale, St. Paul, Minnesota. 



8. A nearly complete, partially exfoliated valve. X 2. 



Ordovician (Mohawkian) Trenton portion of Jacksonburg Is., Jackson- 

 burg, New Jersey. 



Figs. 9, 10. DALMANELLA TESTUDINARIA (Dalman) var 242 



9. A pedicle valve. X 2. 



10. Brachial valve. X 2. 



Ordovician (Mohawkian) Trenton portion of Jacksonburg Is., Jackson- 

 burg, New Jersey. 



Figs. 11-13. HINDIA PARVA (Ulrich) 197 



11. Three specimens showing variations in size. 



12. Vertical section. X 10. 



13. Longitudinal section. X 10. 



Ordovician (Mohawkian) Trenton shales, Fillmore County, Minnesota. 



Figs. 14-16. SCENIDIDM ? MEROPE (Billings) 268 



Ventral side, area, and lateral views of the type. 



Ordovician (Mohawkian) Trenton Is., Ottawa, Ontario. 

 Figs. 17-18. CYRTOLITINA NITIDULA (Ulrich) 311 



Two views of the type. The specimen, although a cast of the interior, 

 preserves the surface markings. X 2. 



Ordovician (Mohawkian) Trenton Is., Covington, Kentucky. 

 Figs. 19, 20. ECCYLIOMPHALUS TRENTONENSIS (Conrad) 306 



Two views of an incomplete specimen. 



Ordovician (Mohawkian) Trenton portion of the Jacksonburg Is., 

 Jacksonburg, New Jersey. 

 Figs. 21, 22. MICROCERAS INORNATUM (Hall) 312 



Side and edge views of a complete shell. X 6. 



Ordovician (Cincinnatian) Maysville group, Cincinnati, Ohio. 

 Figs. 23-26. CYCLORA MINUTA (Hall) 316 



23. View of side and aperture. X 6. 



24. Under side of shell. X 6. 



25. Under side of another specimen showing lip more spreading near umbilicus. 



X 6. 



26. View of side and aperture. X 6. 



Ordovician (Cincinnntian) Maysville group, Cincinnati, Ohio. 

 Fig. 27. CYCLORA HOFFMANN: (Miller) 317 



A complete shell. X 10. 



Ordovician (Cincinnatian) Maysville group, Cincinnati, Ohio. 

 Figs. 28-30. CYCLORA PARVULA (Hall) 316 



28. View of side and aperture. X 8. 



29. Under side of shell. X 8. 



30. Side view of shell illustrating the characteristic angulated first whorl. X 8. 



Ordovician (Cincinnatian) Maysville group, Cincinnati, Ohio. 

 Figs. 31-36. STROPHOSTYLUS TEXTILIS (Ulrich and Scofield) 315 



31. Cast of the interior showing the usual form of the species. 



32. Surface markings of a well preserved specimen. X 5. 



33. Cast of a depressed shell retaining traces of the external markings. 



34. Ventral view of a testiferous example. 



35. Shell in which part of the last whorl was removed to show the spirally- 



twisted plates of the columella. 



36. Dorsal view of the incomplete shell. 



Ordovician (Mohawkian) Trenton shales, St. Paul, Minnesota. 

 Figs. 37-39. SINUITES CANCELLATUS (Hall) 313 



Three views of an entire shell representing the average proportions of 

 the Trenton form of the species. 



Ordovician (Mohawkian) Trenton shales, Chatfield, Minnesota. 

 Figs. 40, 41 SINUITES GRANISTRIATCS (Ulrich) 314 



40. Dorsal view of an average example. 



41. View of aperture of another specimen. 



Ordovician (Cincinnatian) Eden shale, Covington, Kentucky. 



Fig. 42. CONULARIA TRENTONENSIS (Hall) 320 



A nearly complete example. 



Ordovician (Mohawkian) Trenton portion of Jacksonburg Is., Jackson- 

 burg, New Jersey. 

 Fig. 43. TROCHOLITES AMMONIUS (Conrad) 327 



Emmons' illustration of this species. 



Ordovician (Mohawkian) Trenton Is., of New York. 



Figs. 1-5 are after Hall and Clarke; 8-10, 19, 20, 42 are after Weller; 

 6, 7, 11-13 are after Winchell and Schuchert ; 14-16 after Billings; 17, 

 18, 31-41 after Ulrich and Scofleld ; 21-26 after Meek; and 23 after 

 Miller. 



400 



