232 POTTS VILLE FAUNA OF OHIO 



Genus Entolium Meek 

 Entolium attenuatum Herrick 



1887 Entolium attenuatum. Herrick, Bull. Den. Univ., Vol. 2, p. 24, Fig. 11. 

 Coal Measures: Flint Ridge, Ohio. 



Description. Enlolium attenuatum is not at all common among the 

 Pottsville fauna of this State and its known occurrence is confined to 

 the Lower Mercer and McArthur members. It is smooth-shelled, 

 similar in appearance and closely related to E. aviculatus. It differs 

 from the latter species principally in its narrow elongate form which 

 has the height equal to one and one-fourth times the width, while in 

 E. aviculatus the height and width are almost equal. Individuals are 

 most common in occurrence along Flint Ridge, Licking County. 



Dimensions. Length 18 mm., width 13 mm., convexity of single 

 valve 1.5 mm. 



Horizon and locality. Lower Mercer limestone: Muskingum 

 County, Locality 45, r; Licking County, Localities 46, Flint Ridge, 47, 

 48, 49, r; Mahoning County, Locality 55, r. McArthur limestone: 

 Vinton County, Locality 84, r. 



Entolium aviculatus (Swallow) 

 PI. XIII, fig. 9 



1858 Pecten aiiculatus. Swallow, Trans. St. Louis Acad. Sci., Vol. 1, p. 213. 

 Coal Measures: Valley of Verdigris, Kansas. 



Description. This species with its wide stratigraphic and geo- 

 graphic range is the most abundant and characteristic pelecypod of the 

 Lower Mercer limestone. It is present throughout the middle and 

 upper Pottsville, but is nowhere found in such extreme profusion as in 

 the Lower Mercer member; it is also common and widely distributed in 

 the McArthur limestone. It is characterized by its subcircular, com- 

 pressed form with the anterior and posterior parts flattened and sepa- 

 rated from the body of the shell by two furrows extending from the 

 beak to the anterior- and posterior-inferior margins respectively, and 

 also by its smooth, prominent ears. The delicate, concentric markings 

 are generally not preserved so that the surface appears smooth. It is 

 associated with Entolium attenuatum and Crenipecten foerstii, the former 

 being of rare occurrence and the latter very abundant, especially in 

 the Lower Mercer limestone of Muskingum and Licking counties. 



Horizon and locality. Widely distributed throughout the Lowei 

 Mercer and McArthur members, aa. Upper Mercer member: Mus- 

 kingum County, Locality 68, r. Black Flint: Jackson County, Locali- 

 ty 87, r. 



