228 POTTSVILLE FAUNA OF OHIO 



marked by strong radiating ribs crossed by fine concentric lines of 

 growth; posterior ear strongly concave and acutely pointed above, ex- 

 ternally marked by coarse, concentric lines of growth with faint traces 

 of radiating ribs visible on a few specimens. The contour of the ears 

 differs from the figured specimens of A. sorer, but resembles closely that 

 of D. scalaris', the radiating markings are likewise represented as equally 

 strong on both ears. The surface sculpture of the body of the shell 

 consists of about seventeen strong, radiating ribs, slightly nodose in 

 character, separated by two to four finer nodose lirae of varying size, 

 with the interspaces between them wider than the lirae themselves. 

 The entire surface is covered by extremely fine, concentric lines. 



Horizon and locality. Lower Mercer limestone: Muskingum 

 County, Localities 28, 43, 45, r; Licking County, Locality 46, r. 



Genus Deltopecten Etheridge 

 Deltopecten occidentalis (Shumard) 



1855 Pecten occidentalis. Shumard, Geol. Rep. Mo., p. 207, PI. C, Fig. 18. 

 Coal Measures: Near Plattsburg, Clinton County, Missouri. 



Description. This common and widely distributed Pennsylvanian 

 pelecypod makes its appearance in this State in the Boggs limestone 

 and continues throughout the remainder of the Pdttsville formation; 

 it is especially common in the Lower Mercer limestone. It is recog- 

 nized by its subequal ears and its rounded radiating ribs of unequal 

 size which die out at various intervals between the beak and margins; 

 only a comparatively few extend as far as the beak. The Ohio speci- 

 mens are all small, an individual of average size from the Boggs lime- 

 stone measuring: length 20 mm., width 18 mm., length of hinge line 

 15 mm. 



Horizon and locality. Boggs limestone: Muskingum County, Lo- 

 cality 27, r. Widely distributed throughout the Lower Mercer lime- 

 stone, c. Me Arthur member: Jackson County, Locality 80, r; Vinton 

 County, Locality 84, c. 



Deltopecten scalaris (Herrick) 

 PI. XIII, figs. 5,. 6 



1887 Aviculopecten scalaris. Herrick, Bull. Den. Unir., Vol. 2, p. 26, PI. 1, Fig. 8. 

 Coal Measures: Flint Ridge, Ohio. 



Description. Shell of median size, almost equivalve, moderately 

 convex, length and width about equal, maximum length below middle 

 of shell; hinge straight or nearly so, equal to about three-fourths the 



