PLATE XI— Continuea. 



Genus DERBYA, Waagen. 



Page 261. 



Derbya Correana, Derby. 



Fig. 18. Cardinal view of an internal cast of the pedicle-valve ; showing^ the cavities left by the dental 

 lamellse and median septum. 



Fig. 19. The same specimen, viewed from above ; showing the extent of the median septum. 



Fig. 20. Cardinal view of an internal cast having a much higher ai-ea and a somewhat distorted beak. 



Fig. 21. The exterior of a high cardinal area; showing the longitudinally grooved deltidium perforated 

 near the lower part by a small oval foramen, which is probably accidental. From a gutta- 

 percha impression in a natural mould. 



Fig. 22. The interior of a pedicle-valve ; showing the union of the dental lamHllje with the median septum, 

 thus forming a subapical vault. 



Upper Carboniferous. Itaituha, Brazil. 

 For the original illustrations of the two preceding species, see Bulletin of the Cornel! University, 

 Vol. I, No. 2. 



