84 MISSISSIPPIAN BRACHIOPODA 



at an angle of about 130 degrees to the plane of the valve, its lateral mar- 

 gins sharply denned and bearing six oblique spines upon each side of the 

 beak; delthyrium broadly triangular, the deltidium confined to the apex 

 and the lateral margins. Internal characters not observed. 



Brachial valve gently concave posteriorly, becoming more strongly 

 curved towards the anterior and lateral margins; cardinal area about 

 one-half the height of that of the opposite valve, with which its surface 

 'makes a very broad angle, being nearly 180 degrees. The cardinal pro- 

 cess filling the greater portion of the delthyrium of the other valve, the 

 remaining internal characters not observed. 



Surface of both valves marked by fine, regular, radiating costae which 

 increase by bifurcation and intercalation, from 100 to 120, are present 

 about the margin of an average specimen, about five or sometimes six 

 occupying the space of one millimeter, except towards the cardinal ex- 

 tremities where they become finer and more or less obscure, they are also 

 somewhat finer towards the beaks of the valves. 



Remarks. This species has its nearest allies in C, illinoisen$is and G. 

 multicosta. It differs from both these species in its smaller size, and 

 from C. illinoiseiisis it differs in its proportionately more elongate hinge- 

 line, the greatest width of the shell being at the hinge-line. The propor- 

 tional length of the hinge-line is similar to that of C. multicosta but be- 

 sides being a much smaller species it possesses somewhat coarser costse. 

 The species is the only one as yet observed in the Chester faunas, where 

 it is one of the rarer forms. 



Horizon. Chester group, Paint Creek formation. 



CHONETES LOGANI Norwood and Pratten 

 Plate VIII, Figs. 4346 



1855. Chonetes Logani Norwood and Pratten, Jour. Acad. Nat. Sci. Phil. 



(2), vol. 3, p. 30, pi. 2, figs. 12a-c. 



1865. Chonetes Logani Winchell, Proc. Acad. Nat. Sci. Phil., p. 116. 

 1867. Chonetes logani Hall, Pal. N. Y., vol. 4, pi. 22, figs. 23, 26-27. 

 1888. Chonetes logani Herrick, Bull. Sci. Lab. Denison Univ., vol. 3, p. 35, 



pi. 7, fig. 22, pi. 3, fig. 12. 

 1888. Ch&netes logani Herrick, Bull. Sci. Lab. Denison Univ., vol. 3, p. 35, 



pi. 7, fig. 22; pi. 3, fig. 12. 

 1892. Chonetes Logani Hall and Clarke, Pal. N. Y., vol. 8, pt. 1, pi. 16, 



fig. 25. 



1894. Chonetes logani Keyes, Mo. Geol. Surv., vol. 5, p. 53. 

 1901. Chonetes logani Weller, Trans. St. Louis Acad. Sci., vol. 11, p. 182, 



pi. 16, figs. 10-11. 

 1909. Chonetes logani Weller, Bull. Geol. Soc. Am., vol. 20, p. 299, pi. 12, 



figs. 12-13. 



Description. Shell strongly convex, subsemielliptical in outline, the 

 greatest width along the hinge-line, the cardinal extremities acutely an- 



