BRACHIOPODA. 241 



Genus SCENIDIUM,* Hall. 1860. 



PLATE VU A, FIGS. 31-43. 



1846. Orlhis, Rouaclt. Bulletin Soc. Geologique de Prance, '2iul Ser., tome iv, p. 322. 



1848. (h-this, Davidson. Bulletin Soc. Geologique ile France, 2ii(l Sei-., tome v, p. S23. 



1852. Orthis, Hall. PaK-eontology of N. Y., vol. ii, p. 251, pi. li, tig. 2. 



1853. Orthis, Schnur. Zusammenst. und Beschieib. Eifel Bracliiopoiien. 

 1859. Oi-ihli, Salter. Murchison's Siluria, p. 544. 



1859. Orthis, Hall. Paleontology of N. Y., vol. iii, p. 173. 



1860. Orthis, Lindstrom. Gotland's Brachiopodei-, p. 370. 



1860. Skenidium, Hall. Thirteenth Rept. N. Y. State Cat). Nat. Hist., p. 70, tigs. 1-5. 



1861. Skenidium {Ortliis), Hall. Palasontology of N. Y., vol. iii. pi. x a, tigs. 13-15. 



1868. Orthis, Davidso.n. Trans. Geological Society of Glasgow. 



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



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



1871. Orthis, Davidson. British Silurian Brachiopotla, p. 254. pi. xxxviii, tig. 20. 



1871. Orthis, QcENSTEDT. Petrefactenkuude Deutschlands. 



1871. Mystrophora, Kaysbr. Zeitschr. der deiitsch. geolog. Gesellschaft, j). 612, i)l. xiii, tig. 5. 



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



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



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

 1883. Skenidium. Hall. Report of N. Y. State Geologist for 1882, pi. xxxvii, tigs. 29-35. 



(1) 1884. Skenidium. Waloott. Paleontology of Eureka District, p. 116, pi. xiii, tig. 4. 



1887. Sceiiidium. QEhlbrt. Bull. Socit'le d'Etudes Scientiticjues d'Angers, extr., p. 4, pi. v, tigs. 8-10. 

 1887. Skenidium, Tschernyschew. Meinoires Comite Geologiipie, vol. iii, No. 3, pji. 10(), 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 Hat, 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 surftice covered with radiating strias." — 

 Hall, 1860, ut. cit. 



Type, Orthis imignis. Hall. Lower Helderberg group. 



* The customary spelling of this generic term has beea Skenjdidm ; the better form is undoubtedly 

 ScBNiDiOM, as suggested by Dr. (Ehlert. 



