Lowellville limestone. Its surface is ornamented by slender ribs, 

 a little more than their own diameter apart, which are crossed by 

 rather strong, more closely arranged concentric lines. Where the 

 radiating and concentric markings cross each other, little nodes or 

 scales are formed. The ornamentation of the ears is similar to that 

 of the body of the shell. 



Dimensions. Height 6.5 mm., length about 6 mm. 



Horizon and locality. Lowellville member: Poverty Run, Mus- 

 kingum County (Locality 19), r. 



Genus Deltopecten Etheridge 



Deltopecten scalaris (Herrick) 

 PI. V, Figs. 7, 8. 



1887 Aviculopecten scalaris. Herrick, Bull. Den. Univ., Vol. 2, p. 26, PI. 1, Fig. 8. 

 Coal Measures: Flint Ridge, Ohio. 



Description. Shell of medium size, almost equivalve, moderately 

 convex, length and width about equal, maximum length below middle 

 of shell; hinge straight or nearly so, equal to about three-fourths 

 the maximum width of the shell below; cardinal area broad with 

 large, triangular ligamental pit beneath the beaks. Ventral an<^ 

 anterior margins broadly rounded, posterior margin slightly produced 

 below the middle of the shell; ears subequal, sharply defined on either 

 side of the beaks by a sinus which is deeper on the anterior ear than on 

 the posterior; anterior ear slightly convex in outline, posterior ear 

 mucronate at hinge line, strongly concave in outline. Surface marked 

 by fascicles of strongly elevated ribs, three to five in each bundle 

 (generally four) which increase by bifurcation; ears also marked by 

 strong radiating ribs; entire surface including the ears crossed by fine, 

 regular, closely arranged, concentric lines, which form minute scales 

 where they cross the radiating ribs. 



Dimensions. An individual of average size measures: length 

 34 mm., height 33 mm., length of hinge line 22.5 mm; convexity of 

 left valve 5 mm. 



Remarks. Aviculopecten fasciculatus Keyes and A.providencesis 

 Cox are Pennsylvanian species which also have the fasciculate group- 

 ing of the ribs and to which the Ohio Pottsville form can be compared. 

 The former is a much larger species, almost three times as large, 

 and comes from a much higher horizon in the Pennsylvanian system. 

 A.providencesis is likewise a much larger form. If these species could 

 be reduced to the size of D.scalaris, the ribs would probably be larger 

 and less numerous. 



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

 Muskingum County (Locality 26), c. Lower Mercer and higher 

 Pottsville horizons, c. 



78 



