DESCRIPTION OF SPECIES 171 



perfect forms from the Boggs member agree closely with McChesney's 

 description and were identified with 0. capuliformis with more con- 

 fidence. 



Dimensions. The diameter of a small specimen is 7.5 mm.; of a 

 large specimen 18 mm. 



Remarks. The doubtful forms from the Harrison and Sharon 

 horizons may possibly be identical with 0. meekana Whitfield, which 

 is common and widely distributed in the higher Pottsville members of 

 this State, but the material at hand is too crushed to show specific 

 characters adequately. However, 0. meekana has the beak of the 

 dorsal valve eccentric, located about one-third of the length of the 

 shell from the, posterior margin, while that of the specimens under dis- 

 cussion is more central. 0. missouriensis Shumard is in general a 

 much smaller form, and also has the beak eccentric. 



Horizon and locality. Harrison ore: Jackson County, Locality t, 

 r. Sharon horizon: Jackson County, Locality 6, a. Boggs member: 

 Muskingum County, Locality 26, r. 



Orbiculoidea meekana (Whitfield) 



1882 Discina meekana. Whitfield, Ann. N. Y. Acad. Sci., Vol 2, p. 228. 



Coal Measures: Carbon Hill and Flint Ridge, Ohio; Illinois, Iowa. 



Whitfield's description. "Shell of moderate size or larger, circular 

 to subcircular in outline. Dorsal valve convex, with an elevated beak 

 which is directed backward and situated at about one-third of the 

 length of the shell from the posterior margin. Posterior slope slightly 

 concave just below the apex; anterior slope convex. Surface of shell/ 

 when preserved, marked by fine, even, but elevated and regular con- 

 centric lines, with flattened interspaces; about ten or eleven of the 

 elevated lines occupy the space of an eighth of an inch on the middle 

 of the shell, being finer within and coarser beyond that point. On the 

 partially exfoliated shell fine vascular lines are perceptible. Ventral 

 valve flat, discoidal, circular in outline, or perceptibly elongated in 

 some cases; the apex a little more than one-third the length from the 

 posterior margin. Foramen small, elongate-elliptical, narrow, not ex- 

 tending more than one-fourth of the distance from the apex toward 

 the margin, and the depression somewhat further. Surface marked as 

 in the other valve." 



Dimensions. A specimen of average size measures: diameter 18 

 mm., height 8.5 mm. 



Remarks. Orbiculoidea meekana is a common fossil in the middle 

 and upper Pottsville formation above and including the Lower Mercer 

 limestone. The shell belongs to the same general type as 0. missouri- 

 ensis, with which it is commonly considered a synonym, but a number 



