DESCRIPTION OF 'SPECIES 181 



Mercer limestone has the following measurements: length 47 + mm., 

 length of hinge line 40 mm., width 50 + mm. The hinge line is com- 

 monly shorter than the greatest width of the valves, which are marked 

 with fine, sinuous lines. Coarse, concentric wrinkles cover the visceral 

 regions, but become more deeply impressed on the ears. The ventral 

 valve is not marked by a sinus, but sometimes a slight flattening occurs 

 in the mesial region. A few large spines are scattered over the surface. 

 Horizon and locality. Universally distributed throughout the mid- 

 dle and upper Potts ville formation: Lowellville, c; Boggs, a; Lower 

 Mercer, aa; Lower Mercer ore, c; Upper Mercer, aa; Me Arthur, aa; 

 Black Flint, c. 



Productus semireticulatus (Martin) 

 PI. VIII, fig. 6 



1847 Productus semireticulatus. De Koninck, Monog. du Gen. Prod, et Chon., p. 83, 

 PL 8, Figs. 1 a-h; PL 9, Figs, la-m; PL 10, Figs. la-d. 

 Carboniferous: Harrisville, Bagdad, Cuyahoga, Zanesville, Flint Ridge, 

 Greensburg, and Antrim, Ohio; Missouri, Indiana, Illinois, Kentucky; Bo- 

 livia, South America. 



Remarks. This common and widely distributed Productus is one 

 of the most abundant and characteristic fossils of the Pottsville forma- 

 tion of this State, especially in the middle and upper members. In 

 size, however, it is considerably smaller than is generally the rule with 

 representatives of the species. 



Dimensions. A typical specimen measures: length 35 mm., width 

 at hinge line 46 mm., convexity 23 mm. 



Horizon and locality. Lowellville limestone: Muskingum County, 

 Localities 20, 21, c. Widely distributed in the Boggs, c, Lower Mer- 

 cer, Upper Mercer, McArthur, and Black Flint members, aa. 



Productus semireticulatus (Martin) var. 

 PI. VIII, figs. 4, 5 



Compare 1915 Productus morrowensis. Mather, Bull. Den. Univ., Vol. XVIII, p. 152, 

 PL 10, Figs. l-4a. 

 Hale formation: Arkansas and Oklahoma; Morrow formation: Oklahoma. 



Description. Associated with Productus semireticulatus there is 

 another less abundant Productus of the semireticulatus type, which 

 may either represent a distinct species or may be only a variety of the 

 above form. The contour is in no way different, although the size is 

 generally less, and the radiating costae are finer and more regular. 

 Careful comparisons have been made by the writer with the type speci- 



