428 MISSISSIPPIAN BRACHIOPODA 



RETICULARIA COOPERENSIS (Swallow) 

 Plate LXXV, Figs. 21-33 



3860. Spirifer Cooperensis Swallow, Trans. St. Louis Aead. Sci., vol. 1, 



p. 643. 

 1862. Spirifer hirtus White and Whitfield, Proc. Boston Soc. Nat. Hist,, 



vol. 8, p. 293. 

 1865. Spirifera hirtaf Winchell, Proe. Acad. Nat. Sci. Phil., p. 119. 



1869. Spirifera hirtaf Winchell, Safford's Geol. Tenn., p. 442. 



1870. Spirifera hirtaf Winchell, Proc. Am. Phil. Soc., vol. 11, p. 251. 

 1888. Spirifer f hirtus? Herrick, Bull. Sci. Lab. Denison Univ., vol. 3, 



p. 47, pi. 3, fig. 2. 



1888. Spirifer hirtus Herrick, Bull. Sci. Lab. Denison Univ., vol. 4, pi. 10, 

 fig. 20. 



1894. Spirifera cooperensis Keyes, Mo. Geol. Surv., vol. 5, p. 78. 



1895. Spirifer hirtus Hall and Clarke, Pal. N. Y., vol. 8, pt. 2, pi. 38, 



fig. 14. 



1895. Spirifer (c.f.) hirtus Hall and Clarke, Pal. N. Y., vol. 8, pt. 2, pi. 

 84, figs. 36-37. 



1899. Eeticularia cooperensis Girty, Mon. U. S. Geol. Surv., vol. 32, p. 555, 



pi. 70, figs. 9a-c. 



1900. Eeticularia cooperensis Weller, Trans. St. Louis Acad. Sci., vol. 10, 



p. 80, pi. 2, fig. 11. 



3901. Eeticularia cooperensis Weller, Trans. St. Louis Acad. Sci., vol. 11, 

 p. 166, pi. 14, figs. 14-15. 



Description. Shell below medium size, broader than long, subellipiti- 

 cal in outline, the hinge-line much shorter than the greatest width, the 

 cardinal extremities rounded, the lateral margins regularly rounded, the 

 anterior margin gently rounded, sometimes nearly straight in the middle. 

 The dimensions of a nearly perfect individual are : length of pedicle valve 

 17.3 mm., length of brachial valve 15 mm., maximum width 21.3 mm., 

 length of hinge-line 12 mm., thickness 11.9 mm., height of cardinal area 

 21.1 mm. 



Pedicle valve rather strongly convex, the greatest convexity posterior 

 to the middle, the surface curving abruptly from the umbonal region to 

 the cardinal margin, much less abruptly to the lateral margins and more 

 gently to the anterior margin ; mesial sinus originating in the umbonal 

 region, shallow, ill-defined, and rounded in the bottom, sometimes almost 

 or quite obsolete; beak rather small, incurved; cardinal area of moderate 

 height, concave with the curvature increasing towards the beak, the lat- 

 eral margins defined by only a slight angulation of the surface from the 

 lateral slopes of the valve ; delthyrium open, broadly triangular, its width 

 at the base being about one-half the total width of the cardinal area. In- 

 ternally the hinge-teeth are strengthened by a pair of dental lamellae 

 which diverge from the beak in an angle of 20 to 25 degrees or sometimes 

 considerably more and extend along the floor of the valve for about one- 

 fourth its length; between the dental lamella? a median septum extends 



