SCH. SPI.] 



BRA CHIOPODA. 



371 



scars separated by a ridge ; dorsal valve 

 with truncated posterior margin ; two 

 pairs of muscular scars separated by a 

 septum. Type S. truncatus. 

 truncatus, Hall, 1862, (Discina truncata,) 

 16th Rep. N. Y. St. Mus. Nat. Hist., p. 

 28, and Pal. N. Y., vol. 4, p. 23, Gen- 

 esee slate to Chemung Gr. 

 SCHIZOCRANIA, Hall & Whitfield, 

 1875, Ohio Pal., vol. 2, p. 

 73. [Ety. schiza, a cleft; 

 Crania, a genus.] Shell 

 parasitic inequi valve, in- 

 articulated, surface of the 

 upper valve finely stri- 

 ated ; interior with six muscular scars. 

 Type S. filosa. 



filosa, Hall, 1847, (Orbicula (?) filosa,) 

 Pal. N. Y., vol. 1, p. 99, Hud. Riv. and 

 Utica Slate. 



SIPHONOTRETA, DeVerneuil, 1845, Russia and 

 Ural Mountains, vol. 2, p. 286. [Ety. 

 siphon, siphon ; tretos, with a hole in it.] 

 Shell oblong oval, unarticulated ; ven- 

 tral valve most convex with a straight, 

 thick, perforated, conical beak near the 

 hinge-line ; foramen opening on the j 

 back of the beak, and communicating ! 

 with the interior of the shell by a I 

 cylindrical tube or siphon for the pas- 

 sage of the muscle of attachment; dorsal | 

 valve slightly convex, the hinge-line 

 forming an arch which merges imper- 

 ceptibly into the lateral margins; each 

 valve has a wide, crescent-shaped car- 

 dinal edge, covered by horizontal lines 

 of growth; struc- 

 ture calcareo-cor- 

 neous, with a dis- 

 tinctly punctured 

 structure arranged 

 in tubular layers ; 

 surface smooth, 

 with numerous 

 lines of growth and 

 slender hollow spines dilated at the 

 base. Type S. unguiculata. 

 scotica, Davidson, 1877, Geol. Mag., new 



ser., vol. 4, p. 13, Utica slate. 

 SKENIDIUM, Hall, 1860, 13th Rep. N. Y. St. 

 Mus. Nat. His., p. 70. [Ety. skenidian, a 

 little tent.] Distinguished from Orthis 

 by its large triangular area ; the car- 

 dinal process extends as a median sep- 

 tum through the length of the shell, 

 and may be simple or divided at the 

 extremity. Type S. insigne. 

 devonicum, Walcbtt, 1885, Monogr. U. S. 



Geo. Sur., vol. 8, p. 116, Devonian. 

 halli, Safford, 1869, Geo. of Tenn. Not 



defined, 

 insigne, Hall, 1859, (Orthis insignis,) Pa!. 



N. Y., vol. 3, p. 173, Low. Held. Gr. 

 pyramidale. Hall, 1852, (Orthis pyramid- 

 alis,) Pal. N. Y., vol. 2, p. 251, Niag- 

 ara Gr. 



SPIRIFERA. Sowerby. 1815, Mi n. Conch., vol. 

 2, p. 42, and Linmean Trans., vol. 12, 

 p. 514. [Ety. spira, spire ; fero, to bear.] 



FIG. 610. Siphono- 

 treta unguiculata. 

 a, Ventral valve ; 6, 

 interior of same. 



Triangular semicircular, transversely 

 elongate, subglobose or otherwise vari- 

 able in form, with or without mesial 

 fold and sinus ; structure impunctate ; 

 surface smooth, striated or plicated; 

 cardinal line straight, area in each 

 valve ; hinge articulated by short teeth 

 and sockets ; area of the ventral valve 

 larger than the other, and divided by a 

 triangular foramen more or less closed 

 by a false deltidium ; area of the dorsal 

 valve divided in the middle by a fissure 

 occupied by the cardinal muscular pro- 

 cess ; beak of ventral valve more prom- 

 inent than that of the other ; in the in- 

 terior of the dorsal valve the spiral 

 supports of the labial arms are attached 

 by their crurato the hinge plates, some 

 distance from which they are nearly or 

 quite connected by a small process ex- 

 tending inward from each ; the cardinal 

 muscles seem to have been attached to 

 the cardinal process, under and in front 

 of which four scars of the adductor 

 muscles occur ; on each side of a mesial 

 ridge in the ventral valve occur the 

 scars of the adductors, and outside of 

 these the scars of the cardinal muscles. 

 Type S. striata. 



acanthoptera, Conrad, 1842, (Delthyris 

 acanthoptera,) Jour. Acad. Nat.Sci., vol. 

 8, p. 264, Chemung Gr. 



acuminata, Conrad, 1839, (Delthyris 

 acuminata,) Ann. Rep. N. Y., p. 65, and 

 Pal. N. Y., vol. 4, p. 198, Up. Held, and 

 Ham. Grs. 



acuticostata, DeKoninck, 1843, Desc. Ann. 

 Foss. Terr. Garb. Belg., p. 265, Sub- 

 carboniferous. 



agelaia, Meek, 1873, Hayden's Geo. Sur. 

 Terr., p. 470, and White's Cont. to Pal. 

 No. 6, p. 135, Subcarboniferous. 



alata, Castelnau, 1843, Syst. Sil., p. 42. 

 Not recognized. 



albapinensis, Hall & Whitfield, 1877, 

 U. S.Geo. Expl. 40th parallel, vol. 4, p. 

 255, Waverly Gr. 



aldrichi, Etheridge, 1878, Quar. Jour. 

 Geo. Soc., vol. 34, p. 634, Devonian. 



alta, Hall, 1867, Pal. N. Y., vol. 4. p. 248, 

 Chemung Gr. 



amara, Swallow. 1860, Trans. St. Louis 

 Acad. Sci., vol. 1, p. 642, Waverly or 

 Choteau Gr. 



angusta, Hall, 1857, 10th Rep. N. Y. St. 

 Mus. Nat. Hist., p. 164, and Pal. N. Y., 

 vol. 4, p. 230, Ham. Gr. 



annse, Swallow, 1860, Trans. St. Louis 

 Acad. Sci., vol. 1, p. 641, Ham. Gr. 



annectans, Walcott, 1885, Monogr. U. S. 

 Geo. Sur., vol. 8, p. 216, Subcarbonif- 

 erous. 



arata, syn. for S. granulifera. 



archiaci, see S. disjuncta. 



arctica, Haughton, 1857, Jour. Roy. Soc. 

 Dub., vol. 1, p. 183, Devonian. 



arctisegmenta, Hall, 1857, 10th Rep. N. Y. 

 St. Mus. Nat. Hist, p. 131, and Pal. 

 N. Y., vol. 4, p. 208, -Up. Held. Gr. 



