174 POTTSVILLE FAUNA OP OHIO 



more laterally placed pair -of scars, although the possibility exists that 

 they may represent the lateral scars shown in the figure of Lindstroemella 

 aspidium cited above. The median septum is short, extending an- 

 teriorly one-half the length of the visceral area, but dying out a little 

 posterior to it. From the two lateral angles a prominent, elevated 

 (on the internal cast) vascular sinus extends obliquely forward to the 

 anterior-lateral margins of the valve; the sides and front of the shell, 

 as well as the region posterior to the beak, are marked by numerous 

 fine, threadlike, radiating, vascular lines, the coarser ones of which 

 branch from the pair of main sinuses and are subjected to frequent 

 subdivisions. 



Dimensions. The figured specimen of the cotype, preserved as an 

 internal cast upon which the internal structure is imprinted, was ob- 

 tained from the Harrison ore and shows the following .measurements: 

 length 23 mm., width 24 mm., convexity of dorsal valve 5 mm. (much 

 flattened). The measurements of another cotype, which shows the 

 external characters of the shell and the normal convexity are: length 

 22.5 mm., width 23 mm., convexity of dorsal valve 9 mm. This species 

 of Orbiculoidea was also found at one locality in the Sharon ore where 

 it was the only fossil discovered. The size of the Sharon specimens is 

 on the average considerably smaller than that of the forms from the 

 Harrison ore. A large specimen from the Sharon ore measures: length 

 17 mm., width 18 mm., convexity of dorsal valve 4 mm. (somewhat 

 compressed). . 



Remarks. The distinctive features of this species are its circular 

 form, its inconspicuous, depressed beak which overhangs the posterior 

 margin, and its great convexity in the central part of the valve. It 

 resembles 0. meekana Whitfield in form, but the latter species has the 

 beak elevated, forming the point of greatest convexity of the valve; 

 it is also situated farther from the posterior margin, about one-third 

 the length of the shell. 0. munda (Miller and Gurley) and 0. planidisca 

 Raymond are forms which have the beak almost marginal in position. 

 The former is distinctly elliptical in form and has a much less depressed 

 and inconspicuous beak than the species under consideration; the 

 greatest convexity also occurs in the posterior third of the shell. 0. plan- 

 idisca is also elliptical, the width being only three-fourths as great as 

 the length. 



Horizon and locality. Harrison ore: Jackson County, Locality 1, 

 c. Sharon ore: Jackson County, Glen Nell mine, Locality 5, r. The 

 specific name has been given in honor of Mr. Wilber Stout, of the Geo- 

 logical Survey of Ohio. 



Orbiculoidea sp. 



Description. A single minute dorsal valve belonging to the genus 

 Orbiculoidea, which measures 1.3 mm. in diameter, was obtained from 



