BRACH10P0DA. 
261 
Genus DERBY A, Waagen. 1884. 
PLATE X, FIGS. 10-17; PLATE XI, FIGS. 1-5, 18-22; PLATE XlA, FIGS. 23-39; PLATE XIb, FIGS. 1-8,16,17, 23, 24; 
AND PLATE XX. 
1836. Spirifer, Phillips. Illustr. Geology of Yorkshire,, vol. ii, pi. ix, fig. 5. 
1844. Orthis, McCoy. Synopsis Carbonif. Fossils of Shetland, p. 123, pi. xxii, fig. 1. 
1852. Orthis, Owen. Geological Rept. of Wisconsin, Iowa and Minnesota, pi. v, fig. 11. 
1853. Orthisina (partim ). Davidson. Introd. British Fossil Brachiopoda, p. 104. 
1855. Leptcena, McCoy. British Palaeozoic Fossils, p. 452. 
1858. Orthis, Hall. Geology of Iowa, pt. ii, p. 640, pi. xix, fig. 5; p. 173, pi. xxviii, fig. 5. 
1858. Orthisina, Meek and Hayden. Proc. Acad. Nat. Sciences Phila., vol. x, p. 161. 
1860. Oi'this, McChesney. New Palaeozoic Fossils, p. 32. 
1861. Streptorhynchus (partim), Davidson. British Carb. Brachiopoda, p. 124, pi. xxviii, figs. 2-7, 9. 
1864. Hemipronites, Meek and Hayden. Rept. Palaeont. Upper Missouri, p. 26, pi. i. fig. 7. 
1868. Hemipronites, McChesney. Trans. Chicago Academy Sciences, p. 28, pi. i, figs. 5, 6. 
1872. Hemipronites, Meek. Rept. Palaeontology Eastern Nebraska, p. 174, pi. v, fig. 10; pi. vii, fig. 1. 
1873. Hemipronites, Meek and Worthen. Geol. Surv. Illinois ; Palaeont., vol. v, p. 570, pi. xxv, fig. 12. 
1874. Streptorhynchus, Derby. Carboniferous Brachiopoda of Itaituba, p. 32, pis. vii, viii. 
1878. Streptorhynchus, Abich. Bergkalkfauna aus der Araxesenge bei Djoulfa in Armenien, p. 73. 
1S83. Streptorhynchus, Hall. Second Ann. Rept. N. Y. State Geologist, pi. xl, tigs. 10-17; pi. xli, 
figs. 1-3, 18-22. 
1884. Herhyia, Waagen. Palaeontologica Indica, Ser. xiii, vol. i, pt. iv, pp. 576, 591-607, pi. Ii, fig. 1; 
pi. lii, figs. 1-3; pi. liii, figs. 1-5; pi. liv, figs. 1-4; pi. lv, fig. 3. 
1887. Derbya, (Ehlert. Fischer’s Manuel de Conchyliologie, p. 1285; 
' 1887. Hemipronites, Herrick. Bull. Denison University, vol. ii, p. 50, pi. 2, fig. 19. 
Diagnosis. General character of the shell as in Orthothetes. The external 
form is more variable, being usually plano-convex, rarely concavo-convex, the 
pedicle-valve often more elevated and subpyramidal, becoming irregular in its 
growth toward the apex. The interior of the pedicle-valve bears a high median 
septum, extending longitudinally through the center of the muscular area, 
which is from one-third to two-thirds the length of the valve; near the apex 
of the umbonal cavity it unites with the dental plates forming a small trian¬ 
gular chamber beneath the deltidium. In old shells this cavity is often filled 
by a testaceous secretion. The dental plates do not extend to the bottom of the 
rostral cavity except near the apex. 
Brachial valve broad and regularly convex, or sometimes with an undefined 
median depression, and showing a tendency to auriculation. Cardinal area 
linear; the crural plates are abruptly elevated, and unite to form a strong 
erect cardinal process, which is distinctly bilobed at the summit; each lobe 
being slightly notched at the summit and distinctly grooved along the posterior 
face, the grooves uniting in a wider one at the posterior base of the process. 
Midway in their length these crural plates are marked by a transverse ridge 
