PLATE 4. 
Figs. 1, 8, 9, 10. Orthis peloris. 
1. The ventral valve from a gutta-percha cast of an impression in the stone. 
8, 9. Natural casts of the ventral valve. 
10. A natural cast of the dorsal valve. 
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Figs. 2-7. Orthis alstjs. 36 
2. The dorsal valve of this species ? from a gutta-percha cast of an impression of the exterior. 
3. The exterior of a dorsal valve, showing a mesial depression. 
4. A cast of the interior of a ventral valve. 
5. A cast of the interior of a dorsal valve. 
6. A cast of a ventral valve which is nearly flat. 
7. A cast of a dorsal valve, the muscular impressions being scarcely defined. 
Figs. 11-19. Streptorhynchus chemungensis, var. pandora. 68 
11. A cast of the dorsal valve of a young individual. 
12. A gutta-percha cast of an impression of the exterior of a ventral valve. 
13. A cast in stone, of the dorsal valve. 
14. A gutta-percha impression from a cast of the dorsal valve. 
15. A cast of the dorsal valve retaining the shell on the margins. 
16. The cast of a small dorsal valve. 
17. The interior of a ventral valve) from a gutta-percha impression. 
18. The cast of a ventral valve. 
19 A ventral valve which is more finely striate than is usual with this species; probably an 
extreme variety. 
