96 MISSISSIPPIAN BRACHIOPODA 



increase in length towards the cardinal extremities. The beak of the 

 pedicle valve is compressed and flattened, and sometimes slightly dis- 

 torted from attachment in early growth. External surface of both valves 

 marked by exceedingly fine, radiating costae, which are crossed by a 

 double series of oblique concentric lines. The concentric markings are 

 best developed on the brachial valve. 



Remarks. In its general form, and in its cardinal spines this genus does 

 not differ essentially from Chonetes, but it can be distinguished at once 

 from that genus by means of its surface markings. A single species of 

 the genus is known and the condition of preservation in which it has been 

 observed is not such as to allow the internal characters of the shell to be 

 clearly distinguished, but the inner surface of the valves apparently lack 

 the papillae which are so constant a feature in Chonetes. 



CHONOPECTUS FISCHERI (Norwood and Pratten) 

 Plate VIII, Fig. 73 ; Plate LXXXIII, Figs. 21-22 



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



(2), vol. 3, p. 25, pi. 2, fig. 3. 

 1858. Chonetes fischeri Hall, Geol. Iowa, vol. 1, pt. 2, p. 517, pi. 7, 



figs. la-c. 



1869. Chonetes Fischeri Winchell, Safford's Geol. Tenn., p. 443. 



1870. Chonetes Fischeri Winchell, Proc. Am. Phil. Soe., vol. 11, p. 250. 

 1883. Chonetes Fischeri Hall, Rep. N. Y. State Geol. for 1882, pi. (16) 



47, figs. 17-31. 

 1892. Chonopectus Fischeri Hall and Clarke, Int. to Study of Brach., pt. 



1, pi. 20, figs. 24-27. 

 1892. Chonopectus Fischeri Hall and Clarke, Pal. N. Y., vol. 8, pt. 1, pi. 



15B, figs. 20-23 ; pi. 16, figs. 17, 31. 



1900. Chonopectus fischeri Weller, Trans. St. Louis Acad. Sci., vol. 10, 



p. 69, pi. 1, fig. 17. 



1901. Chonopectus fischeri Weller, Trans. St. Louis Acad. Sci., vol. 11, pp. 



150, 151, 154, pi. 12, fig. 1, pi. 13, fig. 17. 



Description. Shell concavo-convex, subelliptical or subcircular in out- 

 line, usually wider than long, the hinge-line usually a little shorter than 

 the greatest width of the shell, the hinge extremities subrectangular or 

 a little rounded. The lateral margins gently convex or nearly straight 

 posteriorly, curving more rapidly towards the front and passing without 

 interruption into the broadly rounded anterior margin. The dimensions 

 of two individuals are : length 17 mm. and 21 mm., width 24.8 mm. and 

 30.8 mm., convexity of pedicle valve 3.5 mm. and 5 mm. 



Pedicle valve most convex near the middle, becoming moderately com- 

 pressed towards the cardinal extremities, with no mesial sinus or mesial 

 flattening of the valve ; the umbonal region usually a little flattened, the 

 beak scarcely protuberant beyond the cardinal margin ; the cardinal mar- 

 gin sharply defined, bearing about four, slender, obliquely curved spines 



