a small wing-like extension; sometimes the posterior margin meets 

 the hinge line at right angles, while more commonly the hinge line 

 is shorter and the posterior-superior angle is truncated and slightly 

 rounded. The surface is marked by strong, regular, concentric lines 

 of growth. 



Remarks. The form resembles that of M .kansasensis Shumard, 

 but lacks the fluted lamellae of that species. It differs from M. 

 recurvirostris Meek and Worthen in its more oblique form and in 

 lacking the prominent, strongly recurved beak which characterizes 

 the latter species. 



Horizon and locality. Boggs limestone in Muskingum County: 

 near Hopewell P.O. (Locality 26), c; Blunt Run (Locality 27), c; 

 Rock Cut (Locality 28), c. Present in higher horizons of the Potts- 

 ville formation in Ohio. 



Myalina pernaformis Cox var. 

 Pi. V, Figs. 5, 6. 



Description. Two small specimens of Myalina from the Harrison 

 ore of Jackson County have been classed as varieties of Myalina 

 pernaformis. The axis is somewhat more oblique and the size much 

 less than that of mature specimens of M .pernaformis from the higher 

 Pottsville horizons. The angle between the cardinal and anterior 

 margins measures about 52 degrees. It can be compared to M.cunei- 

 formis Gurley, but that form is still more oblique and more triangular 

 in outline. 



Dimensions. Length of greatest diameter from beak to posterior- 

 inferior margin 31 mm., width normal to umbonal ridge 16 mm., thick- 

 ness of left valve 7 mm. 



Horizon and locality. Harrison ore: Jackson County (Locality 

 l),r. 



Genus Posidonia Bronn 



Posidonia girtyi n.sp. 

 PL V, Figs, i, 2. 



Description. Sliell large, ovate, compressed; beaks prominent, 

 almost anterior, slightly elevated and incurved over hinge line; great- 

 est convexity in umbonal region, posterior and ventral portions flat- 

 tened; hinge line straight, about three-fifths the length of the shell 

 below; anterior margin almost straight, with small anterior auricle; 

 ventral and posterior margins continuously rounded, truncated above 

 and meeting the hinge line at an obtuse angle; posterior auricle flat- 

 tened, much larger than anterior auricle. Surface marked by numer- 

 ous, strong, regular, concentric wrinkles, separated by broad, rounded 

 furrows. 



Dimensions. The measurements of two cotypes are: 



Length \ . . ,40 mm. 32 mm. 



72 



