DESCRIPTION OF SPECIES 219 



formis Gurley, but that form is still more oblique and more triangular 

 in outline. 



Dimensions. Length of greatest diameter from beak to posterior- 

 inferior margin 31 mm., width normal to umbonal ridge 16 mm., thick- 

 ness of left valve 7 mm. 



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



Myalina recurvirostris var. sinuosa n. var. 

 PI. XI, figs. 10-12 



Description. A variety of Myalina recurvirostris is of common 

 occurrence in the Lower Mercer limestone from a single locality in 

 Coshocton County. It possesses the strongly recurved beak of Meek and 

 Worthen's species but differs in having a much longer hinge line which 

 forms the widest portion of the shell and produces a prominent wing- 

 like extension in the posterior-dorsal part of the shell. Below the 

 hinge line the strong, concentric, rather regular laminae which cover 

 the surface are curved abruptly, following the contour of the posterior 

 wing. Just below the hinge line the posterior margin becomes sinuous, 

 and a broad, shallow, faintly defined depression extends from the beak 

 to this portion of the shell. Meek and Worthen describe the posterior 

 part of M. recurvirostris thus, : "Posterior side compressed; its margin 

 a little convex in outline, ranging nearly at right angles to the hinge 



above m It differs from the variety at hand in its shorter 



hinge line and in its rounded posterior-dorsal angle. 



Dimensions. The average size of the individuals is approximately 

 the same as that of typical M. recurvirostris. An extremely large in- 

 dividual measures: length normal to hinge line 62 mm., width normal 

 to length 47 mm., length of hinge line 61 mm. 



Horizon and locality. Lower Mercer limestone: Holmes County, 

 Millersburg, Locality 51, c. 



Myalina swallovi McChesney 

 PI. XI, fig. 13 



1860 Myalina swallovi. McChesney, Desc. New Pal. Foss., p. 57. 



Coal Measures: Charbonier and 12 miles northwest of Richmond, Missouri. 

 1865 Myalina swallovi. McChesney, 111. New Spec. Foss., PL 2, Fig. 6a-d. 



Remarks. This well known fossil with its wide stratigraphic and 

 geographic range is a rather common member of the middle and upper 

 Pottsville fauna of Ohio. It is generally well preserved and differs in 

 no way from the species as it ordinarily occurs. 



Meek and Worthen, Geol. Surv. 111., Vol. 2, p. 344, PI. 26, Figs. 9a-c, 1866. 



