278 PAL^ONTOLOaY OP OHIO. 



small concentric striae, and sometimes also showing very faint traces of 

 radiating markings. 



Diameter generally about 0.53 inch in mature specimens. 



The radiating markings are so obscure as not to be seen unless care- 

 fully looked for in a favorable light, consequently no attempt was made 

 to put them in the drawings, as this could scarcely be done without giv- 

 ing an exaggerated impression in regard to their distinctness. Ev^n the 

 concentric lines are made rather too distinct in fig. la. The foraminal 

 impression is also a little too narrow and too oblique in fig. Id, where it 

 should extend directly to the center. The specimen from which fig. Ic 

 was drawn has the foraminal impression very narrow, sharp, and ap- 

 parently more like the true slit of a Discina proper than like a mere 

 oval impression with a minute perforation at its outer end, as in the 

 group Orbiculoidea. Consequently, it may possibly belong to a different 

 shell from that represented by fig. Id. 



In regard to the specific affi^nitios of this shell little can be said, as it 

 presents almost no characters at all to distinguish it from several species 

 found in rocks of various ages. I have seen one in our western Coal 

 Measures very closely resembling it. Our figure la shows the concentric 

 strise coarser than represented by the figures of D. Newberryi, given in 

 the Palaeontology of New York, but the specimens vary somewhat in 

 that character. 



Locality and position : The specimens represented by our figures la, Ic, and Id, are 

 from the Cuyahoga shale, a member of the Waverly group of the Lower Carboniferous, 

 while that represented by fig. 16 is in a light-gray, finegramed, arenaceous matrix, 

 from the same group, at Farmington, Ohio. Prof. Hall's typical specimens were 

 found at Cuyahoga Falls and Akron, Ohio. 



Discina (Orbiculoidea?) plecjeites, Meek. 



Plate 14, figs. 2a, h. 



Shell very nearly circular, or slightly longer than wide. Upper valve 

 much depressed; apex but little elevated, obtuse, and placed very near 

 the posterior margin, with a backward inclination, and more depressed 

 than the surface a little in advance of it ; surface only showing fine, ob- 

 scure, irregular lines, and some stronger wrinkles of growth. Internal 

 cast showing a linear impression along the middle of the anterior slope. 

 Under valve unknown. 



Length, 0.93 inch ; breadth, 0.89 inch ; height a little in advance of 

 apex, 0.16 inch; do. of apex, 0.10. 



