42 MISSISSIPPIAN BRACHIOPODA 



Brachial valve imperfectly preserved in the only example observed, 

 the degree of convexity not known, its surface marked by more or less 

 regular, sublamellose, concentric markings similar in form and size to 

 those of the opposite valve, and by very faint radiating costae upon the 

 flattened spaces between the concentric markings. 



Remarks. Only two specimens of this species have been examined 

 by the writer, these being the original types. The best preserved example 

 is the inner surface of a pedicle valve which has been illustrated by 

 Worthen. The second specimen is a fragment of limestone upon which 

 two valves are crushed, partially overlapping, one apparently being a 

 pedicle valve and the other a brachial. In its concentric surface markings 

 the species resemibles 0. Jceokuk, but it differs from that species in its 

 subelliptical rather than subcircular outline. 



Horizon. Keokuk limestone. 



ORBICULOIDEA BATESVILLENSIS Weller 

 Plate I, Figs. 19, 20 



1897. Orbiculoidea batesvillensis Weller, Trans. N. Y. Acad. Sci., vol. 16, 



p. 255, pi. 18, figs. 4-5. 

 1909. Lingulidiscina batesvillensis Girty, Bull. U. S. Geol. Survey No. 377, 



p. 22, pi. 1, figs. 12-12a. 



Description. Shell subcircular or subovate in outline. The dimensions 

 of two individuals, the cotypes, are: length 17 mm. and 16 mm., width 

 15.5 mm. and 17 mm., convexity 3.8 mm. and 3.5 mm. 



Pedicle valve not known. 



Brachial valve depressed convex, subconical, the apex small and in- 

 conspicuous, inclined posteriorly, and situated excentrically from one- 

 fifth to one-seventh the total length of the valve from the anterior margin, 

 the greatest depth of the valve posterior to the apex, in some specimens 

 notably so ; the surface gently convex throughout from the central portion 

 to the margins, except for a short space back of the apex. The surface 

 markings are concentric in arrangement so far as can be determined 

 from the internal casts. 



Remarks. This species was established upon two internal casts of the 

 brachial valve especially characterized by their small apices which 

 are distinctly lower than the greatest convexity of the valve anteriorly. 

 It is possible that the apex of the valve would be somewhat more 

 prominent in specimens preserving the shell itself, but it must always 

 have been inconspicuous as compared with other species of the genus. 



Horizon, Bates ville sandstone, Batesville, Arkansas. 



