PLATE VI A. 



(Figures 7-9, U. l!i-25, 29, 3-2, by K. EMMONS; 1, 2, 13-17, 2«. 27, by G. B. Simpson; 3, 4, 6, by 11. 1>. Whiti'IKLD; 10, :», 31, bj 



J. C. McConnell; 5, 2S, by J. M. Clakkh; 12, copy.) 



Legend, t. Teeth. ii. Anterior adductor scars, 



j. Cardinal proce.ss. a'. Posterior aildiietor scai-s. 



b. Sockets. x. Accessoi-y adductor (brachial valve) 

 fp. Crural plates. r. Diductor scar. 



c. Crura. o. Ovarian markings, 

 dc. Deltidial covering (brachial valve). v. Vascular markings. 



p. Pedicle-muscle. 



RHIPIDOMELLA, CEhlkut. 



Page 203. 



Orthis circulus, H:i!l. 



Figs. 1, 2. Opposite sides of the original specimen of this species. 

 Clinton group. Reynalc's Basin, N. T. 



Orthis oblata, Hull. 

 Fig. 3. The interior of a small bi-achial valve. 



Fig. 4. The interior of a pedicle-valve of the usual dimensions ; showing the muscular area. 

 Lovvei- Helderbei-g gi-oup. Near Clarksrille, N. Y. 

 Foi- further illustration of this species, see Palreontolog.v of New York, Volume III, j)late 10. 



Orthis musculosa, Hall. 



Fig. 5. The interior of a pedicle-valve ; showing the extravagant develo]iment of the diductor scars, the 

 narrow adductors and the large irapre-ssion of the pedicle muscle. 

 Oriskany sandstone. Cumberland, Maryland. 

 For further illustration, see Palaeontology of New York, Volume III, plate xci, tigs. 1-3. 



Orthis peloris, Hall. 



Fig. 6. An internal cast of the pedicle-valve. The area covered by the muscular impressions is unusually 

 restricted though normal for the species. 



Schoharie gi'it. Near Clarksvillc, N. Y. 

 For further illustration, see PalEeontology of New York, Volume IV, plate iv, figs. 1, 8-10. 



Orthis Yanuxemi, Hall. 



(See Plate VI, figs. 14, 15.; 

 Fig. 7. The intericn- of a lu-achial valve, retaining with unusual distinctness the four scars of the adductor 

 muscles. The ridges radiating from the anterior margin of the muscular area, are jirobably 

 of vascular origin. 



Hamilton group. Canandaigna Lake, N. Y. 

 Fig. 8. An internal cast of the pedicle-valve. 



From Drift of the Hamilton grouj). Near Elmira, N. Y. 

 For further illustration, see Paleontology of New Yoi-k, Volume IV, plate vi, tig. 3. 



Orthis Leucosia, Hall. 



(See Plate VI, tig. 16.) 

 Fig. 9. An internal cast of the pedicle-valve, with .strong muscular scars, and showing the pitting of the 

 ovarian spaces (indicating a premature senile condition 1). 



From Drift of the Hamilton group. Near Elmira, N. Y. 



Orthis Penelope. Hall. 



(See Plate VI, figs. 6-13.) 

 Fig. 10. An enlargement of the cardinal area of the brachial valve, giving the structure in detail. X 3. 

 Hamilton group. CanandaAgua Lake, N. Y. 



Orthis. sp. ? (coniptirc 0. Ptnielojje). 

 Fig. 11. A pedicle-valve, from which the shell has partially exfoliated; showing the muscular impressions 

 on the matrix. 



Waverly group. Qranville, Ohio. 



Orthis I\Iichei.ixi, L'Eveill6. 



Fig. 12. View of the brachial valve of a specimen retaining the spines on a portion of its surface. Copit^d 

 from Davidson's Monograph of the Cai-boniferous Brachiojioda, pi. xxx, fig. 7. 

 Carboniferous shales. Gateside, Ayrshire, iSvtitland. 

 For further illustration, see Davidson, Carboniferous Brachiopoda, plate xxx, figs. 6-12. 



Orthis Burlingtonensis, Hall. 



Fig. 13. The exterioi- of a pedicle-valve. 



This species has been regai-ded by Davidson, Mbbk and some other authors aa identical vith 0. 

 Michelini, L'Eveille. A comparison of the American foi-m with authentic figures of the Euro- 

 pean species, shows a degi-ee of diffei-ence inconsistent with the identity claimed. 

 Burlington limestone Sagenilte, Illinois. 

 For further illustration, see Geol. of Iowa, Vul. I, part ii, pi. xii, fig. 4 ; and pi. xx of this volume. 



