1 



PLATE 4. 



Pago 



Figs, 1,8,9, 10. Orthis peloris 34 



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. 



Figs. 2-7. Orthis ALsus 36 



2. The dorsal valve of this species ? from a gutta-percha cast of an impression of the exterior. 

 8. The exterior of a dorsal valve, showing a mesial depression. 



4. A cast of the interior of a ventral valve. 

 6. 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. Streptorhtnchus chemunoensis, 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. 

 16. 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. 



