BRACHIOPODA. 241 



Genus SCENIDIUM,* Hall. 1860. 



PLATE VII A, PIGS. 31^3. 



1846. OrthU, Rouault. Bulletin Soc. Geolog-ique de France, 2nd Sor., tome iv, p. 322. 



1848. Orthis, Davidson. Bulletin Soc. Geologique de France, 2nd Sei-., tome v, p. 323. 



1852. Orthis. Hall. Palieontology of N. Y., vol. ii, p. 251, pi. li, fig. 2. 



1853. Orthis, Schnur. Zusammenst. und Beschreib. Eifel Brachiopoden. 

 1859. Orthis, Salter. Murchison's Siluria, p. 544. 



1859. Orthis, Hall. Paljeontolog-y of N. Y., vol. iii, p. 173. 



1860. Orthis, Lindstrom. Gotland's Brachiopoder, p. 370. 



1860. jSfejiJdifMK, Hall. Thirteenth Rept. N. Y. State Cab. Nat. Hist., p. 70, figs. 1-5. 



1861. Skenidium (Orthis), Hall. PaUeontology of N. Y., vol. iii, \i\. x A, figs. 13-15. 



1868. Orthis, Davidson. Trans. Geological Society of Glasgow. 



1869. Skenidium, Sakford. Geology of Tennessee, p. 287. 



1869. Orthis, Davidson. British Silurian Bi-achiopoda, p. 208, pi. xxv, figs. 4, 9. 



1871. Orthis, Davidson. British Silurian Brachiopoila, p. 254, pi. xxxviii, fig. 26. 



1871. Orthis, Quenstedt. Petrefactenkunde Deutschlands. 



1871. Mystrophoi-a, Kayser. Zeitschr. der deutsch. geolog. Gesellschaft, p. 612, ]il. xiii, fig. 5. 



1872. Oithis, Rigadx. Bulletin Society Academ. de Boulogne. 



1882. iSkmidium, Davidson. British Devonian Brachiopoda. Suppl., p. 49, pi. iii, tigs. 11-14. 



1883. Skenidium, David.son. British Silurian Brachiopoda. Suppl,, pp. 173-175, pi. xi, figs. 1-7. 

 1883. Skejiidium, Hall. Report of N. Y. State Geologist for 1882, i)l. xxxvii, figs. 29-35. 



(1) 1884. /Skenidium, Walcott. PaUeontology of Eureka District, p. 116, pi. xiii, fig. 4. 



1887. Scenidium, CEhlert. Bull. Societe d'Etudes Scientifiipies d' Angers, extr., p. 4, pi. v, figs. 8-10. 

 1887. Skenidium, Tschernyschew. Memoires Comite Geologique, vol. iii. No. 3, pp. 106, 107, pi. iv, 



figs. 13-17. 



Diagnosis. " Shell subpyramidal, somewhat semicircular, with or without 

 median sinus and elevation. Area large, triangular, divided by a narrow 

 fissure, which is sometimes closed at the summit by a concave deltidium. 

 Valves articulating by teeth and sockets, which are often obscure or obsolete. 

 Dorsal valve flat, or varying from depressed-convex to concave. Beak entire, 

 or indented by the foramen ; cardinal line straight and usually equaling the 

 width of the shell ; cardinal plates broad and well developed, marked by the 

 imprints of the peduncular muscles, and produced in the middle in a pointed 

 process ; the cardinal process extends, as a median septum, through the length 

 of the shell, and may be simple or divided at its [anterior] extremity. Ventral 

 valve elevated, subpyramidal; beak straight or slightly arched; muscular im- 

 pressions undetermined. Exterior surface covered with radiating striae." — 

 Hall, 1860, ut. cit. 



Type, Orthis insignis, Hall. Lower Helderberg group. 



* The customary spelling of this generic term has htmw Skenidium ; the better form is undoubtedly 

 Scenididm, as suggested by Dr. ffiHLBRT. 



