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, 6, by It. P. Whitfield; 10, 30, 31, by 
J. C. McConnell; 5, 28, by J. M. Clarke; 12, copy.) 
Legend, t. Teeth. 
j. Cardinal process. 
b. Sockets. 
fp. Crural plates. 
c. Crura. 
dc. Deltidial covering (brachial valve), 
p. Pedicle-muscle. 
a. Anterior adductor scars, 
a'. Posterior adductor scars, 
x. Accessory adductor (brachial valve) 
r. Diductor scar, 
o. Ovarian markings, 
v. Vascular markings. 
Figs. 
Fig. 
Fig. 
Fig. 
Fig. 
Fig. 
RHI PIDOMELL A, CEhlert. 
Page 208. 
Orthis circulus, Hall. 
1, 2. Opposite sides of the original specimen of this species. 
Clinton group. Reynale's Basin, N. Y. 
Orthis oblata, Hall. 
3. The interior of a small brachial valve. 
4. The interior of a pedicle-valve of the usual dimensions ; showing the muscular area. 
Lower Helderberg group. Ntar Clarksville, N. Y. 
For further illustration of this species, see Palaeontology of New York, Volume III, plate 10. 
Orthis musculosa, Hall. 
5. The interior of a pedicle-valve ; showing the extravagant development of the diductor scars, the 
narrow adductors and the large impression 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. 
6. An internal cast of the pedicle-valve. The area covered by the muscular impressions is unusually 
restricted though normal for the species. 
Schoharie grit. 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.; 
7. The interior of a brachial valve, retaining with unusual distinctness the four scars of the adductor 
muscles. The ridges radiating from the anterior margin of the muscular area, are probably 
of vascular origin. 
Hamilton group. Canandaigua Lake, N. Y. 
8. An internal cast of the pedicle-valve. 
From Drift of the Hamilton group. Near Elmira, N. Y. 
For further illustration, see Palaeontology of New York, Volume IV, plate vi, fig. 3. 
Orthis Leucosia, Hall. 
(See Plate VI, fig. 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 structure in detail. X 3. 
Hamilton group. Canandaigua Lake, N. Y. 
Orthis, sp. ? (compare O. Penelope). 
Fig. 11. A pedicle-valve, from which the shell has partially exfoliated ; showing the muscular impressions 
on the matrix. 
Waverly group. Gh'anville, Ohio. 
Orthis Michelini, L’Eveill6. e 
Fig. 12. View of the brachial valve of a specimen retaining the spines on a portion of its surface. Copied 
from Davidson’s Monograph of the Carboniferous Brachiopoda, 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 O. 
Michelini, L’Eveille. A comparison of the American form with authentic figures of the Euro¬ 
pean species, shows a degree of difference inconsistent with the identity claimed. 
Burlington limestone Sageville, Illinois. 
For further illustration, see Geol. of Iowa, Vol. I, part ii, pi. xii, fig. 4; and pi. xx of this volume. 
