median in position. A specimen from the Harrison ore measures: 

 length 14.5 mm., height 14 mm., convexity of left valve 4.5 mm. 



Horizon and locality. Harrison ore: Jackson County (Locality 

 1), r. Common in Lower Mercer and Me Arthur limestones. 



Schizodus wheeled Swallow 



1858 Schizodus obscurus. Swallow, Trans. St. Louis Acad. Sci., Vol. 1, p. 193. 



(Not Aximus obscurus Sowerby, 1823.) 



Lower Permian, Kansas. 

 1872 Schiodus wheeleri. Meek, U. S. Geol. Surv. Nebr., p. 209, PI. 10, Figs. la-f. 



Upper Coal Measures: Missouri, Nebraska, Iowa. 



This species is common in the middle and upper Pottsville rocks 

 of Ohio, but has not been found below the Boggs horizon. Specimens 

 are generally in a good state of preservation so that their identifica- 

 tion is made with a considerable degree of confidence. 



Horizon and locality. Boggs member: near Hopewell P.O., 

 Muskingum County (Locality 26), c. Common in middle and upper 

 Pottsville. 



Genus Aviculopecten McCoy 



Aviculopecten coxanus Meek and Worthen 



I860 Avicnlopecten coxanus. Meek and Worthen, Proc. Acad. Nal. Sci. Phil. p. 453. 

 Coal Measures: Adams County, Illinois. 



Common throughout the Pottsville formation of Ohio, but abun- 

 dant in the Lower Mercer limestone. The radiating ribs, which 

 alternate in size, are on the whole finer with wider interspaces than 

 indicated on Herrick's figured specimen from the Lower Mercer 

 limestone of Flint Ridge. l The form is slightly oblique with large 

 ears which are also marked by radiating ribs. The entire surface 

 is covered with fine, closely arranged, concentric lines. 



Dimensions. A large specimen from the Sharon ore measures: 

 length 13.5 mm., length of hinge line 10 mm., maximum width below 

 hinge line 13 mm. 



Horizon and locality. Harrison ore: Jackson County (Locality 

 1), r. Sharon ore: Lick Run, Scioto County (Locality 2), c. Lowell- 

 ville limestone: Poverty Run, Muskingum County (Locality 19), c. 

 Boggs limestone: Blunt Run, Muskingum County (Locality 27), c. 

 Abundant in the Lower Mercer and upper Pottsville. 



Aviculopecten pellucidus Meek and Worthen 

 I860 Aviculopecten pellucidus. Meek and Worthen, Proc. Acad. Nat. Sci. Phil., 



p. 455. 



Coal Measures: Adams County, Illinois. 

 1866 Aviculopecten pellucidus. Meek and Worthen, Geol. Surv. 111., Vol. 2, p. 327, 



PI. 26, Figs. 5a, b. 



Lower Coal Measures: Adams County, Illinois. 



Description. A single specimen of this small, delicately sculp- 

 tured Aviculopecten was found in the black shale associated with the 



iHerrick, C. L., Bull. Den. Univ., Vol. II, pi. 1, Fig. 17, 1887. 



77 



