PLATE VIA. 



(Figures 7-9, 11, 18-25, 29, 32, by E. Emmons; 1, 2, 13-17, 26, 27, by G. B. Simpson; 3, 4, e, by It. P. Whitfield; 10, 30, 31, bj 



J. C. McConnell; 5, 28, by J. M. Clarke; 12, copy.) 



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



j. Cardinal process. a'. Posterior adductor scai-s. 



b. Sockets. x. Accessory adductor (brachial valve) 

 fp. Crural plates. r. Diductor scar. 



c. Crura. 0. Ovarian mai-kings. 

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



p. Pedicle-muscle. 



RHIPIDOMELLA, CEhlert. 



I'age 203. 



Okthis circulus, HtiU. 



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

 Clinton group. Reynale's Basin, N. Y. 



Orthis oblata, Hall. 

 Fig. 3. The interior of a small bi'achial vah-e. 



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

 Lower Helderbei'g gi-oup. Near Clarksinlle, iV. T. 

 For further illustration of this species, see Palteontology of New York, Volume III, jjlate 10. 



Orthis musculosa, Hall. 



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

 nari-ow adductors and the large impression of the pedicle muscle. 

 Oriskany sandstone. Cumberland, Maryland. 

 For further illustration, see PalEBontology 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 Clarksville, N. Y. 

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

 Orthis Vanuxemi, Hall. 

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

 Fio-. 7. The interior of a brachial valve, retaining with unusual distinctness the foui' scars of the adductor 

 muscles. The ridges radiating from the anterior mai'gin of the muscular area, are probably 

 of vascular origin. 



Hamilton group. Canandaigua Lake, N. Y. 

 Fig. 8. An internal cast of the pe<iicle-valve. 



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

 For further illustration, see Paleontology of New Yoi-k, Volume IV, plate vi, fig. 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 ?). 



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 sti'ucture in detail. X 3. 

 Hamilton group. Canandaigtia Lake, N. Y. 



Orthis, sp. ? (compare 0. Peneloj)e). 

 Fig. 11. A pedicle-valve, from which the shell has pai-tially exfoliated; shovnng the muscular impressions 

 on the matrix. 



Waverly group. Granville, Ohio. 



Orthis Michelini, L'Eveill6. 



Fig. 12. View of the bi-achial valve of a specimen retaining the spines on a portion of its surface. Copied 

 fi'om Davidson's Monograph of the Carboniferous Bi-achiopoda, pi. xxx, fig. 7. 

 Carboniferous shales. Gateside, Ayrshire, Scotland. 

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



Orthis Burlingtonensis. Hall. 



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



This species has been regarded by Davidson, Meek and some other authors as identical vith 0. 

 Michelini, L'Eveille. A compai-ison of the American form with authentic figures of the Euro- 

 pean species, shows a degree of diffei'ence inconsistent with the identity claimed. 

 Bui-lington limestone Sageville. Illinois. 

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



