Remarks. A single, well preserved specimen was found in the 

 Lowellville limestone, but the species occurs rather commonly in the 

 Lower Mercer and McArthur members. The Ohio specimens are on 

 the average larger than those figured by Meek but in other respects 

 the forms are identical. The measurements of the specimen from the 

 Lowellville limestone which is among the largest found, are: length 

 9.7 mm., height 9.5 mm., length of hinge line 7 mm. One from the 

 Lower Mercer limestone measures: length and height 5 mm., length 

 of hinge line 4.2 mm. 



Horizon and locality. Lowellville member: Poverty Run, Mus- 

 kingum County (Locality 19), r. Common in the Lower Mercer 

 and McArthur limestones. 



Genus Pleurophorus King 

 Pleurophorus tropidophorus Meek 



1875 Pleurophorus tropidophorus. Meek, Pal. Ohio, Vol. 2, p. 338, PI. 19, Figs. 

 10 a, b. 

 Coal Measures: Newark, Ohio. 



Meek's description: "Shell transversely oblong, much compressed, 

 with length a little greater than twice the height; posterior margin 

 flattened and bifurcated, the lower truncation being nearly vertical, 

 and the upper sloping obliquely downward and backward from the 

 hinder end of the hinge; cardinal margin straight, equaling about 

 two-thirds the length of the valves; anterior rounded below and slop- 

 ing abruptly forward from the beaks above; basal margin long, parallel 

 to the hinge, nearly straight for most of its length, or faintly sinuous 

 near the middle, rounding up anteriorly, and forming a more or less 

 defined angle at its connection with the lower part of the posterior 

 margin behind; posterior umbonal slope distinctly angular from the 

 beaks to the angular posterior basal extremity, while a second carina 

 passes obliquely backwards and downwards along the middle of the 

 posterior dorsal space above the umbonal ridge of each valve; beaks 

 depressed to the line of the cardinal margin, very little projecting, 

 and placed one-fifth to one-fourth the length of the valves from the 

 anterior margin. Surface marked by distinct concentric lines of 

 growth, that become strongly defined on the flanks and anterior parts 

 of the valve, but are less distinct on the space above and behind the 

 umbonal angles." 



Dimensions. A specimen of typical size from the cannel coal 

 mine on Flint Ridge, Licking County, measures: length 29.5 mm., 

 maximum height posterior to the beak 15 mm., convexity of a single 

 valve 4 mm. 



Remarks. This species is rare below the Lower Mercer lime- 

 stone but is fairly common and widely distributed in the latter and 

 higher members, especially the McArthur limestone. The species 

 shows very little variation from place to place, and differs from Meek's 

 figured specimen only in having the beak slightly more depressed. 



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