232 MISSISSIPPIAN BRACHIOPODA 



Remarks. The punctate structure of the shell is commonly rather 

 obscure in examples of this species which have come under observation. 

 The internal structures of the rostral portion of the brachial valve, how- 

 ever, especially the undivided hinge-plate, always seem to be present in 

 specimens which are clearly punctate, and it is believed that they are 

 all congeneric. 



Horizon. Kinderhook. 



RHYNCHOPORA BEECHERI Greger 

 Plate XXIX, Figs. 31-38 



1904. Rkynchopora beecheri Greger, Am. Geol., vol. 33, p. 297, figs. 4-9. 

 1910. Rhynchopora beecheri Weller, Bull. Geol. Soc. Am., vol. 21, p. 515. 



Description. Shell below medium size, triangularly subovate in outline, 

 subpyramidal in form, broader than long in adult individuals, the greatest 

 breadth near the mid-length of the shell. The postero-lateral margins 

 nearly straight or gently convex, meeting at the beak in an obtuse angle, 

 the lateral margins rounded, the anterior margin usually nearly straight. 

 The dimensions of a nearly complete internal cast are : length 10.5 mm., 

 width 12.8 mm., thickness 10 mm., width of sinus in front 8 mm. 



Pedicle valve depressed convex in the umbonal region with the surface 

 flattened or gently convex towards the antero-lateral margins, the serrate 

 lateral margins abruptly deflected towards the opposite valve ; along the 

 median line the surface is gently convex to near the anterior border of 

 the shell and is there abruptly curved towards the opposite valve; the 

 mesial sinus originates near or a little back of the middle of the valve 

 as a rather broad, shallow depression, usually a little convex trans- 

 versely across the bottom, becoming gradually deeper anteriorly and 

 curving rather abruptly towards the opposite valve as it approaches the 

 anterior margin of the shell, produced in a broad lingual extension with 

 a nearly straight and deeply serrate distal margin whose surface in front 

 lies in nearly a right angle to the plane of the valve; the beak rather 

 broad and but little incurved, perforated by a subcircular foramen; the 

 delthyrium broadly triangular and nearly filled by the beak of the oppo- 

 site valve; plications rounded or subangular, simple, originating in the 

 umbonal region on internal casts but probably continuing to the beak 

 upon the surface of the shell, from four to six occupy the sinus and 

 from five to eight each lateral slope. Internally the hinge-teeth are 

 supported by a pair of dental lamellae which extend from one-third to 

 one-half the length of the valve. 



Brachial valve much more convex than the pedicle, becoming gibbous 

 anteriorly in adult specimens, the surface slopes from the point of greatest 

 convexity posteriorly in a long convex curve which increases towards the 

 beak, and in a short, more abrupt curve to the anterior margin, trans- 



