PLATE XI b. 
(Figures 2-17, 20-24 by G. B. Simpson; 1,18,19 by E. Emmons.) 
Legend, j. Cardinal process. rv. Rostral vault. 
d. Dental lamellae. dr. Dental ridges, 
t. Teeth. 
Genus DERBYA, Waagen. 
Page 261. 
(See Plates X, XI and XIa.) 
Derbya, sp. indet. 
Fig. 1. The interior of 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. Kansas City, Missouri. 
Derbya cymbula, sp. nov. 
Fig. 2: Cardinal 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 the apex of the pedicle-valve shows evidence of 
the existence of a median septum. 
Fig. 3. View of the brachial valve of the same specimen; showing its form, contour 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 pronounced in both valves. 
Upper Coal Measures. Near Kansas City, Missouri. 
Derbya Kaskaskiensis, McChesney. 
Fig. 6. The interior of an imperfect pedicle-valve, in which the median septum unites with the dental 
lamellae, forming an elongate deltidial or rostral vault, like that seen in Derbya Correana, Derby 
(plate xi, fig. 22). 
Chester limestone. Crittenden county, Kentucky. 
Derbya robusta (?), Hall. 
(See Plate X, figs. 12-17.) 
Fig. 7. The interior of a brachial valve of an old shell, which probably belongs to this species. The 
cardinal 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 vascular sinu- 
• ses. The outline at the left .shows the convexity of the valve. 
Upper Coal Measures. Winterset, Iowa. 
Fig-. 8. The interior of a pedicle-valve, having a comparatively harrow 5 cardinal area, a relatively small 
flabellate muscular impression, and a short median septum. 
Upper Coal Measures. Near Kansas City, Missouri. 
Genus STEEPTORHYNCHUS, King. 
rage 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 impressions of the 
brachial valve. X 8. 
Figs. 10, 11, 12. Anterior, profile and cardinal 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 ai'ticulated 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. 
