214 MISSISSIPPIAN BRACHIOPODA 



TETRACAMERA SUBCUNEATA (Hall) 

 Plate XXVIII, Figs. 13-24 



1856. Rhynchonella subcuneata Hall, Trans. Albany Inst., vol. 4, p. 11. 

 1858. Rhynchonella subcuneata Hall, Geol. Iowa, vol. 1, pt. 2, p. 658, 



pi. 23, figs. 3a-c. 

 1863. Rhynchonella perrostellata Swallow, Trans. St. Louis Acad. Sci., 



vol. 2, p. 85. 



1882. Rhynchonella subcuneata Whitf., Bull. Am. Mus. Nat. Hist., vol. 



1, p. 51, pi. 6, figs. 47-49. 



1883. Rhynchonella subcuneata Hall, 12th Rep. Geol. Surv. Ind., p. 333, 



pi. 29, figs. 47-49. 



1894. Camaropharia subcuneata Hall and Clarke, Int. to Study of 

 Brack, pt. 2, pi. 45, figs. 3-4. 



1894. Rhynchonella subcuneata Keyes, Mo. Geol. Surv., vol. 5, p. 102. 



1895. Camarophoria subcuneata Hall and Clarke, Pal. N. Y., vol. 8, pt. 



2, pi. 62, figs. 34-37. 



1906. Camarophoria subcuneata Beede, 30th Ann. Rep. Geol. Surv. Ind., 



p. 1304, pi. 22, figs. 47-49. 

 1910. Tetracamera subcuneata- Weller, Bull. Geol. Soc. Am., vol. 21, p. 



503, fig. 4. 



Description. Shell below medium size, the valves subequally convex, 

 subtriangular in outline, usually broader than long, the greatest width 

 near the anterior extremity, the long postero-lateral margins straight or a 

 little concave, usually meeting at the beak in an acute angle. The dimen- 

 sions of two examples are : length 11.7 mm. and 10.4 mm., width 12 mm. 

 and 11.5 mm., thickness 7.3 mm. and 6.3 mm. The dimension of the 

 largest example observed are : length 15.3 mm., width 15.3 mm., thickness 

 9.6 mm. 



Pedicle valve depressed-convex, the surface gently arched from the 

 beak to the anterior margin except in old shells in which the valve is 

 rather abruptly deflected anteriorly to meet a similar deflection of the 

 opposite valve, along the postero-lateral margin the valve is abruptly 

 deflected towards the opposite valve, the deflected portion on each side 

 forming about one-half of a smooth, flattened or slightly concave region 

 on each side of the beak; mesial sinus obsolete posteriorly and repre- 

 sented anteriorly only as a slight, indefinite flattening of the valve which 

 sometimes cannot be detected at all ; beak small, sharply pointed, slightly 

 incurved, the delthyrium triangular, open towards the apex but closed 

 below by the beak of the opposite valve ; plications angular, from 12 to 

 20 in number, either simple or dividing near the beak, in no case is 

 the bifurcation upon the body of the shell a conspicuous feature. 



Brachial valve similar in form to the pedicle, the surface arched 

 from the beak to the anterior margin, the curvature being strongest near 

 the beak, the postero-lateral margins deflected to meet the similar de- 

 flected portion of the opposite valve and to take part in the formation 



