PLATE 8. 
Fig. 1. Orthis leonensis?. 
I. Cast of ventral valve. 
Fig. 2. Orthis thiemei. ?... 
2 Cast of the ventral valve. 
Figs. 3-8. Orthis leonensis. 
8. A dorsal valve. 
4, 5. Casts of dorsal valves. 
6, 7. Casts of ventral valves. 
8. Exterior of a ventral valve. 
Figs. 9, 10. Orthis leucosia?. 
9, 10. The exterior of a dorsal valve and cast of the ventral valve. 
Figs. 11 -19. Orthis imrressa.... 
II, 12. Casts of ventral valves of young individuals. 
13. A dorsal valve retaining the shell. 
14. Cast of a dorsal valve, showing muscular impressions and vascular lines. 
15. Ventral valve retaining the shell. 
16-18. Casts of ventral valves of the usual forms. 
19. A cast of an unusually large specimen of a ventral valve. 
Figs. 20-29. Orthis tioga. 
20-23. Illustrations of the dorsal valve. 
24, 25. Casts of the dorsal valve retaining impressions of the surface striae. 
26, 27. Ventral valves showing the mesial elevation. 
28, 29. Casts of the ventral valve, showing muscular impressions. 
Figs. 30-32. Orthis carinata. 
30. Cast of a ventral valve of this species. 
31. A dorsal valve with the shell partly exfoliated. 
32. A cast of the dorsal valve showing the form of the muscular impression. 
Page 
02 
63 
62 
60 
59 
58 
