PLATE XI—Continued. 
Genus DERBY A, 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 
lamellae 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 area 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 lamellae with the median septum, 
thus forming a subapical vault. 
Upper Carboniferous. Itaituba, Brazil. 
For the'original illustrations of the two preceding species, see Bulletin of the Cornell University, 
Vol. I, No. 2. 
