1897.] NEW YORK ACADEMY OF SCIENCES. 255 



Beachiopoda. 



OrBICULOIDEA BATESVILLENSIS Sp. nOV. 



PI. XIX., figs. 4-5. 



Shell subcircular or longitudinally subelliptical in outline. 

 Brachial valve depressed conical, with the apex situated at a 

 point a little DQ,ore than one-half the distance from the center 

 to the posterior margin, and directed backward. 



Surface ornamented with faint concentric lines of growth. 



This species is similar to 0. newberryi, Hall,* from the Cuya- 

 hoga shale of Ohio, but is less circular and much larger. 



Streptorhynchus williamsi sp. nov. 

 PL XIX., figs. 1-3. 



Shell large, irregularly subcircular or transversely sub-ellipti- 

 cal in outline. Hinge-line shorter than the greatest width of the 

 shell. 



Pedicle valve irregularly convex, a little wider than long. 

 Beak elevated, distorted, inclined posteriorly at an angle of 

 about 45°. Dental lamellre reduced to rounded ridges which 

 bound the delth3'rium laterall}-. Median septum absent. 



Brachial valve wider than long, regularly convex, the greatest 

 convexity being well towards the beak. Cardinal process promi- 

 nent, more or less deeply bilobed. 



Surface ornamented with numerous, fine, bifurcating, radiating 

 strice. Strong, irregular wrinkles of growth are present on the 

 pedicle valve, but are lacking on all the specimens of the brachial 

 valve which have been examined. 



In the genus Streptorhynchus^ as restricted by Hall and Clarkf 

 to include only those streptorhynchoid shells possessing a promi- 

 nent bifid cardinal process in the brachial valve, and no median 

 septum in the pedicle valve, only a single American species has 

 heretofore been recognized, S. ulrichi, H. & C.| This species 

 is not perfectly known, but *S'. williamsi may be readily dis- 

 tinguished from it on account of its much greater size. 



Unfortunately all the Arkansas specimens are more or less frag- 

 mentary, two of the most perfectly preserved ones being figured. 

 No specimen shows the beak of the pedicle valve complete, but 

 enough is preserved to show that no median septum is present. 

 The form of the cardinal process is extremely variable. Figure 



*Pal., N. Y., Vol. IV., p. 25, PI. I., figs. 10-11. 



t Pal. N. Y., Vol. 8, pt. 1, p. 267. 



t Pal. N. Y., Vol. 8, pt. 1, p. 351, PI. XI. B, fig. 15. 



