BRACHIOPODA. 241 



Genus SCENIDIUM,* Hall. 1860. 



PLATE VII A, FIGS. 31-43. 



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



1848. Ortkis, Davidson. Bulletin Soc. Geolog-ique de France, 2nd Ser., tome v, p. 323. 



1852. Orthis, Hall. Paljeontolog-y 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. Palseontology of N. Y., vol. iii, p. 173. 



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



1860. 8ke7udium, Hall. Thirteenth Rept. N. Y. State Cab. Nat. Hist., p. 70, tigs. 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. Skenidium, Safford. Geology of Tennessee, p. 287. 



1869. Orthis, Davidson. British Silurian Brachiopoda, p. 208, pi. xxv, tigs. 4, 9. 



1871 . Orthis, Davidson. Bi'itish 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, tig. 5. 



1872. Orthis, Rigaux. Bulletin Society Academ. de Boulogne. 



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



1883. Skenidium, Davidson. British Silurian Brachiopoda. Suppl., pp. 173-175, pi. xi, tigs. 1-7. 

 18S3. Skenidium, Hall. Report of N. Y. State Geologist for 1SS2, pi. xxxvii, figs. 29-35. 



(?) 1884. Skenidium, Walcott. Palaeontology of Eureka District, p. 116, pi. xiii, fig. 4. 



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

 1887. Skenidium, T.schernyschew. 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 fiat, 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 haaa Skenidwm ; the better form is undoubtedly 

 Scenidium, as suggested by Dr. CEhlert. 



