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-defined marginal ridge marks the straight cardinal margin. 

 The surface is smooth except for a few thin, elevated lines parallel 

 to the ventral and posterior margins. 



Remarks. This species is rare in the Pennsylvanian rocks of 

 Ohio, and there is no record of its occurrence at any horizon as com- 

 monly as it does in the Boggs member. The type specimen was 

 obtained from the Upper Coal Measures of Nebraska, at which horizon 

 it also occurs in Iowa and Missouri. Meek, however, described and 

 figured the same species from the Lower Coal Measures of Ohio, but 

 he does not state the exact horizon and locality from which the fig- 

 ured specimen came. Herrick also figures a form from Flint Ridge 

 in Licking and Muskingum counties (Lower Mercer) which he pro- 

 visionally refers to this species. 1 



Horizon and locality. Boggs limestone, near Hopewell P.O., 

 Muskingum County (Locality 26), c. Lower Mercer. 



Genus Myalina DeKoninck 



Myalina pernaformis Cox 

 PL V, Figs. 3, 4. 



1857 Myalina pernaformis. Cox, Geol. Kept. Ky., Vol. 3, p. 569, PL 8, Fig. 8. 

 Coal Measures: Providence, Hopkins County, Kentucky. 



Description. This form is not rare in the Pottsville rocks of 

 Ohio, but is particularly common and characteristic of the Boggs 

 and Black Flint members. In size it varies within wide limits from 

 very large specimens to immature ones which are about one-half 

 the size of that figured by Cox. The following measurements of 

 individuals selected from the Boggs and Black Flint members will 

 illustrate this variation in size. In the latter member the species 

 attains an unusually large size. 



Boggs Black Flint 

 Length of greatest diameter, from 



beak to posterior-inferior 



margin 22 mm. 48 mm. 60 mm. 69 mm. 



Width, normal to umbonal ridge . . 10 mm. 21 mm. 30.5mm. 35.5 mm. 



Length of hinge line 12 mm. 21 mm. 28 -}-mm. 44 mm. 



Convexity of left valve 3 mm. 6 mm. 10 mm. crushed 



Anterior margin straight, forming an angle of 60 to 65 degrees 

 with the hinge line, subparallel to posterior margin; posterior margin 

 slightly convex in outline, rounding broadly into the front below 

 the middle of the shell. Sometimes the posterior end of the hinge 

 line is somewhat produced with the posterior-lateral margin directly 

 below slightly constricted, so that the posterior-superior angle forms 



iHerrick, C. L., Bull. Den. Univ., p. 38, pi. 1, Fig. 20, 1887. 



71 



