PLATE XI B. 



(Figures 2-17, 20-24 by G. B. Simpson; 1, is, 19 by E. Emmons.) 



Leg'end. j. Canlinal process. rv. Rostral vault, 



(i. Dental lamella;. dr. Dental lidges, 

 t. Teeth. 



Genus DERBYA, Waagen. 



Page 261. 



(See Plates X, XI and XIa.) 



Derbya, sp. iiulet. 



Kijf. 1. The interior iif a large and very convex brachial valve; showing the cardinal process and short, 

 vertical crural plates, from the base of which a thickened ridge extends about the muscular 

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

 Upper Coal Measures. Kaiisas City, Missouri. 



Derbya cymbula, sp. nov. 



l''ig. 2. Cai-dinal view of a large individual, somewhat incomplete at the apex ; showing the height of the 

 area, the median groove on the surface of the deltidium, and the tendency to irregular growth 

 in the pedicle-valve. The broken .surface at th(; apex of the pedicle-valve shows evidence of 

 the existence of a median septum. 



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

 the sui'face ornamentation. 



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

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

 Upper Coal Measures. Near Ka/nsas City, Missouri. 



Derbya Ka.skaskiensis, McChe.sncy. 



Fig. li. The interior of an imperfect pedicle-valve, iu which the median septum unites with the dental 

 lamellse, forming an elongate deltidial or i-ostral vault, like that seen in Derbya Correana, Derby 

 (plate xi, tig. 2'2). 



Chester limestone. Crittenden county, Kentucky. 



Derbya robusta (?), Hall. 



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

 Fig. 7. The interior of a brachial valve of .an old shell, which jirobably belongs to this species. The 

 cardinal process is much thickened and slightly irregular in its growth, the niusculai' area deeply 

 excavated but not well defined, and the pallial region covei'ed with ti'aces of the vascular sinu- 

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

 Ujiper Coal Measui'es. Winterset, Iowa. 

 Fig. 8. The interior of a pedicle-valve, having a conijiaratively narrow caT'dinal ai'ea, a relati\ely small 

 flabellate mnscular impiession, and a short median septum. 

 Upper Coal Measures. Near Ka^isas City, Missouri. 



Genus STKEPTOEHYNCHUS, King. 



Page 267. 



Streptorhynchus pelargonatus. Sflilotlicim. 



Fig. It. An internal cast of the two valve.s; showing- the position of the deltidinm and dental ridges of 

 the pedicle-valve, the inner face of the canlinal iii'ocess, and the nuiscidar impressions of the 

 brachial valve. X '^■ 



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

 contour and general external I'har.'icters of the species. X 2. 



Fig. 13. An intei'nal ca.st of the pedicle-valve ; showing the form of the mu.scnlar ai'ea, without evidence 

 of a median septum. X 2. 



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

 surface of the deltidium, the i-ardinal process, crural plates and the chariicter of the articula- 

 tion. X 5. 



Permian Formation. Posneck, Silesia. 

 For f\uther illustration, see GKiNrrz, Dyas, plate xvi, figs. 26-34 ; Davidson, Permian Brachiopoila, 

 plate ii, tigs. 32-42. 



