BRACHIOPODA. 
241 
Genus SCENIDIUM,* Hall. 1860. 
PLATE VII A, FIGS. 31-43. 
1846. Orthis, Rouault. Bulletin Soc. Geologique de Prance, 2nd Ser., tome iv, p. 322. 
1848. Orthis, Davidson. Bulletin Soc. Geologique de France, 2nd Ser., tome v, p. 323. 
1852. Orthis, Hall. Palaeontology 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. Palaeontology of N. Y., vol. iii, p. 173. 
1860. Orthis, Lindstrom. Gotland’s Brachiopoder, p. 370. 
1860. Skenidium, Hall. Thirteenth Rept. N. Y. State Cab. Nat. Hist., p. 70, figs. 1-5. 
1861. Skenidium (Orthis), Hall. Palaeontology of N. Y., vol. iii, pi. x a, figs. 13-15. 
1868. Orthis, Davidson. Trans. Geological Society of Glasgow. 
1869. ISkenidium, Safford. Geology of Tennessee, p. 287. 
1869. Orthis, Davidson. British Silurian Brachiopoda, p. 208, pi. xxv, figs. 4, 9. 
1871. Orthis, Davidson. British Silurian Brachiopoda, p. 254, pi. xxxviii, fig. 26. 
1871. Orthis, Quenstedt. Petrefactenkunde Deutschlands. 
1871. Mystrophora, Kayser. Zeitschr. der deutsch. geolog. Gesellschaft, p. 612, pi. xiii, fig. 5. 
1872. Orthis, Rigaux. Bulletin Societ6 Academ. de Boulogne. 
1882. Skenidium, Davidson. British Devonian Brachiopoda. Suppl., p. 49, pi. iii, figs. 11-14. 
1883. iSkenidium, Davidson. British Silurian Brachiopoda. Suppl., pp. 173-175, pi. xi, figs. 1-7. 
1883. Skenidium, Hall. Report of N. Y. State Geologist for 1882, pi. xxxvii, figs. 29-35. 
(?) 1884. Skenidium, Walcott. Palaeontology of Eureka District, p. 116, pi. xiii, fig. 4. 
1887. Scenidium, OEhlert. Bull. Societe d’Etudes Scientifiques 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 strise.”— 
Hall, 1860, ut. cit. 
Type, Orthis insignis, Hall. Lower Helderberg group. 
* The customary spelling of this generic term has been Skenidium ; the better form is undoubtedly 
Scenidium, as suggested by Dr. CEhlert. 
