Horizon and locality. Of general distribution in the ' Lowellville 

 (a) and Boggs (c) members; abundant and widely distributed in the 

 Lower Mercer and higher members of the Pottsville formation. 



Genus Chonetes Fischer 



Chonetes choteauensis Mather 

 PL III, Figs. 11, 12 



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

 Figs. 9-1 Oa. 

 Morrow formation: near Choteau and Fort Gibson, Oklahoma. 



Description. Shell small, subcircular to subquadrangular in 

 outline; ratio of length to width about 3:5, hingeline 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, widening 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 nodose appearance when examined micro- 

 scopically. 



Dimensions. A specimen of average size from the Lowellville 

 member measures: length 6.2 mm., width 10.2 mm., convexity 1 mm. 

 The measurements of another specimen from the Boggs limestone, 

 where the form is on^the average larger than in the Lowellville lime- 

 stone, are: length 8.5 mm., width 12 mm., convexity 2 mm. 



Remarks. In the Boggs member this species occurs most com- 

 monly as internal casts on which the muscular impressions and other 

 internal markings are often well preserved. The Ohio forms differ 

 from the typical C. choteauensis from Oklahoma in being less convex, 

 with the mesial sinus or flattening correspondingly less pronounced. 

 These variations, however, may be attributed largely to compression. 

 It is abundant in the Lowellville and Boggs members, and in the 

 former constitutes the most characteristic fossil. 



Horizon and locality. Lowellville limestone: Poverty Run, 

 Muskingum County (Locality 19), a; near Holbein, Muskingum 



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