DESCRIPTION OF SPECIES 



211 



Description. Parallelodon tenuistriatus is a common fossil through- 

 out the Pottsville formation of this State, but it occurs in especial 

 abundance in the Harrison ore and in the Lower Mercer and McArthur 

 members. Forms from the Harrison ore and the McArthur limestone 

 are unusually small and diminutive, while in the Lower Mercer and 

 other horizons a much larger size is attained as may be seen by the fol- 

 lowing measurements: 



Lower 



Specimens of average size Harrison Mercer McArthur 



Length 14.5mm. 29mm. 17mm. 



Height 6mm. 13.5mm. 8mm. 



Thickness of single valves 3mm. 6mm. 4mm. 



Horizon and locality. Harrison ore: Jackson County, Locality 1, 

 a. Boggs member: Muskingum County, Locality 27, r. Widely dis- 

 tributed throughout the Lower Mercer and McArthur members, a. 

 Upper Mercer member: Perry County, Locality 62, r; Muskingum 

 County, Locality 68, r; Coshocton County, Locality 70, r. Black Flint 

 member: Vinton County, Locality 92, r. 



Genus Aviculopinna Meek 

 Aviculopinna americana Meek 



1866 Aviculopinna pinnaeformis. Geinitz, Die Garb, und Dyas in Nebr., p. 31, 



Tab. 2, Fig. 13. (Non Solen pinnaeformis Geinitz, 1848.) 

 Nebraska City, Nebraska. 



1867 Aviculopinna americana. Meek, Am. Jour. Sci., 2nd Ser., Vol. 44, p. 282. 

 1872 Aviculopinna americana. Meek, U. S. Geol. Surv. Nebr., p. 197, PL 9, Figs. 12a-d. 



Upper Coal Measures: Nebraska City, Nebraska; Iowa. 



Description. Internal casts of Aviculopinna americana are fairly 

 common in the Boggs member of Muskingum County, and have also 

 been found in the Lower Mercer limestone along Flint Ridge, Licking 

 County. Specimens are on the average very similar in size and con- 

 tour to the one figured by Meek from the Lower Coal Measures of this 

 State. 1 However, some of the forms from the Boggs limestone are 

 much larger, the largest individual measuring, if restored, about 3.25 

 inches (or 82 mm.). As nearly as can be judged from the crushed con- 

 ditiori of the shells, the original convexity was great and the valves 

 were flattened just below the cardinal margin. The beak is minute and 

 not quite terminal, with the anterior margin extending beyond it in a 

 small pointed lobe; a well denned marginal ridge marks the straight 



Meek, F. B., Pal. Ohio, Vol. II, p. 337, PL 20, Fig. 2, 1875. 



