1897.] NEW YORK ACADEMY OF SCIENCES. 263 



Surface nearly smooth, but showing a few obscure lines of 

 growth. 



This species somewhat resembles M. swallovi, McChesney. a 

 common coal measure species, but is more oblique, with a less 

 prominent umbonal ridge which curves dorsall}^ rather than 

 ventrally towards the posterior extremity, and has an arcuate 

 rather than a sinuate ventral margin. 



LiTHOPHAGA ? BATESVILLENSIS Sp. UOV. 



PI. XX., figs. 14-15. 



Shell of medium size or less, elongate ovate in outline. Ver^' 

 convex anteriorly, somewhat depressed posteriorly. Beaks ter- 

 minal, depressed. 



Hinge-line straight, about three-fifths the total length of the 

 shell. Anterior margin sharply rounded. Ventral margin gently 

 arcuate with the curvature increasing towards the extremities, 

 bending upward and sharply rounded posteriorly into the poste- 

 rior margin, which curves forward, meeting the cardinal line at 

 an obtusely rounded angle. 



Surface nearly smooth, a few inconspicuous lines of growth 

 being distinguishable. 



The species most nearly allied to this is L.pertenuis^M. & W.,* 

 described from the Warsaw beds of the St. Louis limestone. 

 The Arkansas specimens constantly diff'er from that species in 

 having the greatest posterior extension of the shell nearer the 

 ventral margin. 



AVICULOPECTEN BATESVILLENSIS Sp. nOV. 



PI. XX., figs. 3-4. 



Right valve unknown. Left valve of medium size. Exclusive 

 of the wings, broadly sub-ovate in outline, nearly equilatei'al. 

 Length and breadth about equal, the greatest convexity at a 

 point about one-third the distance from the beak to the ven- 

 tral margin, equal to about one-fourth the length. Beak moder- 

 ately elevated above the hinge-line and situated a little anterior 

 to its middle point. 



Hinge-line equal to the greatest breadth of the shell below. 

 Anterior, ventral and posterior margins, to the junction with 

 the wings, sub-circular in outline. 



Wings subequal, anterior one being somewhat the smaller, 

 flat and triangular, abruptly compressed from the umbonal slope. 



*Geol. Surv. Ill , Vol. 5, p. 539, PI. 22, fi?. 1. 



