PLATE VI A. 



(Figures 7-9, 11, 18-25, 29, 32, by E. Emmons; 1, 2, 13-17, 2ti, 27, by G. B. SiMl'S()>f ; 3, 4, ti, by I{. P. Whitkikld; 10, 30, 31, by 



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



Legend, t. Teeth. a. Anterior a(i(lu(-tor scars, 



j. Cardinal process. a'. Posterior adductor scars. 



b. Sockets. x. Acces.sory adductor (l)rachial valve) 

 fp. Crural plates. r. Diductor st^ar. 



c. Crura. o. Ovarian niarkinga. 

 dc. Deltidial covering (brachial valve). v. Vascular niai'kings. 



p. Pe<licle-muscle. 



RHIPTDOMELLA, CEhlkrt. 



Page 203. 

 OUTHIS CIRCULUS, Hull. 

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

 Clinton group. ReynnJe'f: Basin, N. Y. 



Oktius oblata, Hall. 



Fig. 8. The intei-ior of a small Iii-achial valve. 



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

 Lower Helderberg group. Near Clarksville, N. Y. 

 For further illustration of this species, see Palaeontology of New York, Volume III, plate 10. 

 OUTHIS MUSCULOSA, Hall. 

 Fig. 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 farther 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 covei-ed by the musi^dar impressions is unusually 

 restricted though normal for the species. 



Schoharie grit. Near Clarksville, N. Y. 

 For further illustration, see Palseontology of New Yoi-k, Volume IV, plate iv, figs. 1, 8-10. 



Orthis Vanuxemi, Hall. 



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

 Fig. 7. The interior of a brachial valve, retaining with unusual distinctness the four scars of the adductor 

 muscles. The i-idges radiating from the anterior margin of the muscular area, are probably 

 of vascular origin. 



Hamilton group. Canandaigua Lake, N. Y. 

 Fig. 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 Y'ork, 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 scai-s. 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. Canandaigua Lake, N. Y. 



Orthis, sp. ? (compare 0. Pvudope). 

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

 on the matrix. 



Waverly group. Gh-anmlle, Ohio. 



Orthis jNIichelini, L'Eveill6. 



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 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 authoi-s as identical vith O. 

 Micheliui, L'Eveille. A comparison of the American form with authentic figures of the Euro- 

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

 Burlington limestone Sageville, Illinuis. 

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



