178 POTTS VILLE FAUNA OP OHIO 



j 



Deltopecten scalaris, all of which are common and represent a peculiar 

 local fauna, distinct from the Lower Mercer fauna found elsewhere in 

 the State. 



Dimensions. The dimensions of a dorsal and a ventral valve of 

 average size are: 



Dorsal Ventral 



Length 53mm. 58 +mm. 



Width ._. 66mm. 69mm. 



Length of hinge line 52 mm. 52 mm. 



Convexity 13 mm. (Crushed) 8 mm. (Crushed) 



Horizon and locality. Lower Mercer limestone: Scioto County, 

 Vernon Township, Locality 31, c; Licking County, Bald Knob, Lo- 

 cality 46, r. 



Genus Chonetes Fischer 



Chonetes choteauensis Mather 



< 



PI. VII, figs. 16-18 . 



1915 Chonetes choteauensis. Mather, Bull. Den. Univ., Vol. XVIII, p. 150, PI. 8, 

 Figs. 9-10a. 

 Morrow formation: Near Choteau and Fort Gibson., Oklahoma. 



Description. Shell small, subcircular to subquadrangular in out- 

 line; ratio of length to width about 3:5; hinge-line equal to or slightly 

 greater than the greatest width of the shell below. Ventral valve 

 moderately convex, the greatest convexity being anterior to the middle 

 of the valve and on either side of the shallow mesial sinus; ears flat- 

 tened; extremities of the hinge line on some specimens slightly mucro- 

 nate, on others just equal to the greatest width anteriorly; lateral 

 margins forming an angle of 90 degrees with the hinge line, subparallel 

 to a point below the middle of the valve, broadly rounded into the 

 front; front flattened or very slightly concave; beak inconspicuous, not 

 extending beyond the cardinal margin; cardinal area narrow with upper 

 margin marked by four or five long, slender oblique spines on either 

 side of the beak; a poorly defined, shallow mesial sinus, or rather a mere 

 flattening becoming evident in the posterior half of the valve, widen- 

 ing toward the front. Dorsal valve concave, following the curvature of 

 the opposite valve. Surface marked by Very fine, rounded, radiating 

 striae, crossed by concentric lines of growth which are fairly prominent 

 near the anterior and lateral margins; finely punctate with spine bases 

 arranged at regular intervals along the striae imparting to them a no- 

 dose appearance when examined microscopically. 



Dimensions. A specimen of average size from the Lowellville 



