PLATE XiA— Coutinueil. 



Derbya crassa, Meek iiiul Huydon. 

 (See Plate X, tigs. 10, 11 ; and Plate XIu, &gs. 23, 24.) 

 Fig. 2S. The interior of a small brachial valve. 



Fig. 29. The caniinal process of the same specimen, enlarg-ed ; showing the lobation at its sinnniit anil the 

 extent of the crural plates. X 3. 



Upper Coal Measures. Kansas Citji, Missouri. 

 Fig. 30. The extei'ior of a laiger pedicle-valve. 



Fig. 31. The interioi- of a small pedicle-valve; showing the median septum ami large muscular scars. 

 Fig. 32. The interior of a large and old pedicle-valve ; showing the median septum, the thickeniTig about 

 the muscular area, due to age, and marks of vascular sinuses. 

 Upper Coal Measui-es. Winterset, Iowa. 

 Fig. 33. The interior of a large brachial valve which is referi-ed to this species with some doubt. The 

 crural plates are well produced, partially enclo.sing arVmrescent .scais of the adductor muscles. 

 The valve is unusually convex for one of this species. 



Upper Coal Measures. Kansas City. Missouri. 



For other illustrations, see Palseontology of Eastern Nebi'aska, jilate \-. tig. 10, and plate viii, 

 fig. 1. 



Derbya Bennetti, sp. uov. 



Fig. 34. The exterior of a pedicle-valve which letains the scar ol altachnieut at the umbo. 



Fig. 3.5. The opposite side of the same specimen ; showing the height of the cardinal area of the pedicle- 

 valve and the median sinus on the brachial valve. A Crania is attached to the apex of the 

 latter valve. 



Fig. 3(5. Profile view of another specimen. 



Fig. 37. Cardinal view of the same; showing the high cardinal area and the la<-k of .symmetry in the i>ed- 

 icle-valve. 



Fig. 38. The same specimen after having the pedicle-valve cut hoi-izontally near the hinge. The section 

 shows the unsu)>poi'ted dental ridges, the tips of the grooved caniinal process, and the extrav- 

 agant development of the median septum. 



Fig. 39. A similar section of the same specimen near xhe apex. Here the median se|itiun is coalesced with 

 a solid callosity filling the apical portion of the deltidial cavity. 

 Upper Coal Measures. Kansas City, Missouri. 



