ventral valve is not marked by a sinus, but sometimes a slight flatten- 

 ing occurs in the mesial region. A few large spines are scattered 

 over the surface. 



Horizon and locality. Universally distributed throughout the 

 Lowellville (c) and Boggs (c) members; abundant in the middle and 

 upper Pottsville members. 



Productus semireticulatus (Martin) 



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

 p. 83, PI. 8, Figs, la-h; PI. 9, Figs. la-d. 



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

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

 Bolivia, South America. 



Description. This common and widely distributed Productus 

 is one of the most abundant and characteristic fossils of the Pottsville 

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

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

 with members of the species. A typical specimen measures: length 

 35 mm., width at hinge line 46 mm., convexity 23 mm. 



Horizon and locality. Lowellville limestone: near Holbein, 

 Muskingum County (Locality 20), c; Symmes Ford, Muskingum 

 County (Locality 21), c. Boggs: universally distributed in the lime- 

 stone phase, c. Abundant and widely distributed in the Lower Mercer 

 and upper Pottsville horizons. 



Productus semireticulatus (Martin) var. 



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 form of the semireticulatus type, which may 

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

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

 size is generally less and the radiating costae finer and more regular. 



Careful comparisons have been made by the writer with the 

 type specimens of P. morrowensis Mather, borrowed for this purpose 

 from the Walker Museum at the University of Chicago, and with 

 one exception, no essential differences between the two forms could 

 be noted. However, indications of the double row of spines on the 

 cardinal slopes and main flanks which characterizes the Morrow 

 species, were noted on only one of the Ohio specimens although a 

 considerable amount of material was examined. It seems probable 

 that this form represents an individual variation, rather than that 

 the spines were originally present on all the specimens but were not 

 preserved. But it may be added that none of the material at hand 

 is in a first class condition, and that there is a gradual gradation be- 

 tween this form on the one hand and P. semireticulatus on the other. 



52 



