Orac. 



502 



Vol. 7, 1883, p. 257, pi. 25, figs. 3 a, fragment of fish-spine, 

 showing back (?) border ; 3 5, seen from the right (?) side ; 3 cj, 

 restored cross section. Chester (sub-carb.) limestone, — XL 



Oracanthus vetustus, Leidy. (Figures included with those 

 of 0. rectus above.) Jour. Acad. Nat. Sci. Phila., 2d Ser. Vol. 

 3, 1854. St. J. & W., Geo. Sur. 111., Vol. 7, 1883, p. 255, pi. 24. 

 figs. 2 a, right side of the fish-spine ; 2 5, (?, cross sections of it 

 showing thickness of walls of pulp-cavity ; 2 d^ enlarged tuber- 

 cle. St, Louis limestone,, Mo. — XL, 



Orhicula oorrugata. See Crania corrugata. Vl, 



Orhicula crassa. See Obolella crassa. M. C, 



Orbicula excentrica, found by Emmons in the white, 



A.» friable shales of Virginia, L. Sil. or Cambrian, with 

 Lingula striata,, etc.. Am. Geol. Vol. 1, pt. 2, p. 112, 



pj 1^^ pi. 1, fig. 4.-7, or C. 



Orhicula Mosa, See Schizocrania fllosa. LLL a,, LLLh, 

 Orhicula grandis. See Discina grandis. VLLL c, 

 Orhicula lamellosa. See Discina circe. LL c. 

 Orhicula lodensis. See Discina lodensis. VLLL e, 

 Orhicula {lodensis?) Rogers, p. 829, found with Goniatites 



interruptus^ in Penna. See note, but no figure. VLLL e, 

 Orhicula minuta. See Discina minuta. VILL\, 

 Orhicula nitida. See Discina nitida. XLLl, 

 Orbicula parmulata. Hall, p. 48, fig. 6, 4. Medina forma- 



jv^^^ tion. LV, 



^^^B Orhicula squamceformis. See Pholidops squa- 

 ^^*^^ miformis. 



Orhicula terminalis. See Trematis terminalis. LLc, 



Orbicula . Rogers, Geol. Pennsylvania, 1858. p. 818, 



ILIj .rf^^^^fe^ fig. 603. Trenton formation, LLc 



Orbicula - 



— . Emmons, Geol. 

 Second District N. Y., 

 1843, p. 312, fig. 54, 6. 

 Trenton limestone. LI 



