110 The American Geologist. February, 1897 
Fig. 17. Longitudinal, median, section, with the parts of the valves 
analyzed. Leptajna bed. (N. B. Part of the line bounding the pedi- 
cle callist lost in the development of the plate.) 
Fig. 18. Natural cast of the interior of a small ventral valve. Lep- 
taena bed. 
Fig. 19. Cast taken from the interior of a large ventral valve, Leptse- 
na bed. 
Numbers 15, 16 are from Granger, the others from Spring Valley, 
Minnesota. 
Orthis multisecta Meek, figs. 20 to 23. 
Fig. 20. Dorsal view of a specimen, Cincinnati shales, Cincinnati, O. 
Fig. 21. Analyzed ventral plication of same. 
Fig. 22. Lateral profile of same. 
Fig. 23. Median longitudinal section. 
Orthis meeki S. A. Miller, figs. 24 to 29. 
Fig. 24. Ventral view of a specimen found with O. multisecta Meek. 
Fig. 25. Lateral profile of average specimen, Madison, Indiana. 
Fig. 26. Longitudinal median section of one like the last. 
Fig. 27. Analysis of ventral plication of another specimen. 
Fig. 28. Cast taken from interior of ventral valve. 
Fig. 29. Interior of dorsal valve. 
Number 24 is from Cincinnati, O., the others are from Madison, In- 
diana. 
Plate V. 
Orthis ignota, n. sp., figs. 1 to 7. 
Fig. 1. Ventral view of young specimen. 
Fig. 2. Ventral view of average size. 
Fig. 3. Analysis of ventral plication of the last. 
Fig. 4. Lateral profile of same specimen. 
Fig. 5. A longitudinal median section, analyzed. 
Fig. 6. Natural cast of ventral valve, interior. 
Fig. 7. Dorsal valve, interior. 
All are from the Leptaena bed. Spring Valley, Minnesota. 
Orthis tersa Sardeson, figs. 8 to 13. 
Fig. 8. Dorsal view of typical si)ecimen. 
Fig. 9. Analysis of ventral plication of the same. 
Fig. 10. Lateral profile. 
Fig. 11. Longitudinal section. 
Fig. 12. Cast taken of interior of ventral valve, partly restored. 
Fig. 13. Interior of dorsal valve, partly restored. 
All are from the topmost Hudson strata at Wilmington, Illinois. 
Orthis emacerata Hall, figs. 14-18, 28. 
Fig. 14. Dorsal view of an average specimen, Lepta^na bed. 
Fig. 15. Ventral plication of the same specimen. 
Fig. 16. Lateral profile of an avei-age specimen. 
Fig. 17. Median, longitudinal section, Lei^ta^na bed. 
