PLATE XI B. 



(Figures 2-17, 20-24 by G, B. ftiiii'suN; 1, 1«, la by E. Emmons.) 

 Lef^end. i. Cardinal proce8P. i-v. Rostral vault, 



d. Dental lamellae. dr. Dental ridges, 



t. Teeth. 



Genus DERBY A, Waagen. 



Page 261, 



(See Plates X, XI and XIa.) 



Derbya, sp. indet. 



Fig-. 1. The interior of a lai'ge and very convex brachial valve ; showing: the cardinal process and short, 

 vertical crural plates, from the base of which a thickened i-idge extends about the muscular 

 area. The accompanying outline profile shows the convexity of the valve. 

 Upper Coal Measures. Katisas City, Missouri. 



Derbva cymbula. sj). nov. 



Fig. 2. Cardinal view of a large individual, somewhat incomplete at the apex; showing the height of the 

 area, the median gi-oove on the surface of the deltidium, and the tendency to in-egular growth 

 in the pedicle-valve. The broken surface at the apex of the pedicle- valve shows eridence of 

 the existence of a median septum. 



Fig. 3. View of the Iii-achial valve of the same specimen ; showing its form, contoui- and the character of 

 the surface ornamentation. 



Figs. 4, 5. Cardinal and profile views of a small individual, probably belonging to the same species. In 

 this specimen the irregular growth is very pi-onounced in both valves. 

 Upper Coal Measures. Near KaTisas City, Missouri. 



Derbya Kaskaskiensis, McChesney. 



Fig. ti. The interior of an imperfect pedicle-valve, in which tUe median beptum unites with the dental 

 lamellfE, foi-ming an elongate deltidial or rostral vault, like that seen in Derbya Correana, Derby 

 (plate xi, tig. 22). 



Chester limestone. Crittenden county. Kentucky. 



Derbya robusta (?), Hall. 



(See Plate X, figs. 12-17.) 

 Fig. 7. The interioi' of a brachial valve of an old shell, which probably belongs to this species. The 

 cai'dina! process is much thickened and slightly irregular in its growth, the muscular area deeply 

 excavated but not well defined, and the pallial region covered with traces of the va.scular sinu- 

 ses. The outline at the left shows the convexity of the valve. 

 Upper Coal Measures. TVinterset, Iowa. 

 Fig. 8. The interioi' of a pedicle-valve, having a comparatively narrow cardinal area, a relatively small 

 flabellate muscular impression, and a shoi-t median septum. 



Upper Coal Measures. Near Kansas City, Missouri. 



Genus STREPTORHYNCHUS, King. 



I'ugl; 267. 



Streptorhynchus pelargonatus, Schlotheim. 



Fig. 9. An internal cast of the two valves ; showing the position of the deltidium and dental ridges of 

 the pedicle-valve, the inner face of the cardinal process, and the muscular impi'essions of the 

 brachial valve. X 3. 



Figs. 10, 11, 12. Anterior, profile and cai-dinal views of a specimen which retains the shell ; showing the 

 contour and general external characters of the species. X 2. 



Fig. 13. An internal cast of the pedicle-valve ; showing the form of the muscular area, without evidence 

 of a median septum. X 2. 



Fig. 14. The interior of the cardinal portion of the articulated valves ; showing the dental ridges and inner 

 surface of the deltidium, the cardinal process, crural plates and the character of the articula- 

 tion. X 5. 



Permian Formation. Posneck, Silesia. 

 For further illustration, see Geinitz, Dyas, plate xvi, figs. 26-34 ; Davidson, Permian Brachiopoda, 

 plate ii, figs. 32-42. 



