PLATE XI— Continucil. 



Genus DERBYA, Waagen. 



Page 261. 



Derbya Correana, Derby. 



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



lamellse and median septum. 

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

 Fig, 20. Cardinal view of an internal cast having a much higher area and a somewhat distoi-ted beak. 

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



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



pei'cha impression in a natural mould. 

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



thus forming a siibapical vault. 



Upper Carboniferous. Itaitula, Brazil. 

 For theloriginal illustrations of the two preceding species, see Bulletin of the Coraell University, 



Vol. I, No. 2. 



