DESCRIPTION OP SPECIES 243 



forms identified in this bulletin as A. concentrica. The species resembles 

 closely both A. vera and especially A. concentrica. It differs from 

 Hall's figured specimens of the former species in having the beaks less 

 anterior and slightly less prominent, and the surface sculpture more 

 regular. The resemblance to A. concentrica is so close that it has been 

 suggested both by Meek 1 and by Girty 2 that it may represent a variety 

 of the latter rather than a distinct species. Comparisons with A. 

 concentrica as interpreted by Girty show that A. newberryi is less convex, 

 a little narrower, with the dorsal margin more oblique, and with the 

 posterior-inferior angle more produced; the concentric ridges are also 

 more numerous, about twenty-five to twenty-eight being present on an 

 adult individual. The entire surface is covered by extremely fine con- 

 centric lines, and the posterior and basal margins are generally crenulated 

 with radial markings which characterize the middle layer, of shell sub- 

 stance. In view of the differences cited above it seems advisable for 

 the present to- retain the rank of a distinct species for this form, rather 

 than to include it as a variety of A. concentrica. 



Dimensions. Adult individuals attain a considerably larger size 

 than those here referred to A. concentrica. A typical form measures: 

 length 16.5 mm., height at beak 12 mm., convexity of left valve 3.5 mm., 

 length of umbonal ridge 15.5 mm. 



Horizon and locality. Lower Mercer limestone: widely distrib- 

 uted in Muskingum and Licking counties, c. Me Arthur limestone: 

 Vinton County, Locality 84, c. 



Astartella varica McChesney 

 PI. XIV, figs. 1-4 



1860 Astartella varica. McChesney, Desc. New Pal. Foss., p. 55. 

 Coal Measures: Springfield, Illinois. 



Description. This species is common in the middle and upper 

 Pottsville formation, particularly in the Lower Mercer and McArthur 

 members. Eight to ten sharply elevated concentric ridges, separated 

 by broad, rounded furrows, are present. The convexity is moderate 

 and the umbonal slope on uncrushed specimens prominent. A number 

 of individuals from the McArthur limestone show the same interesting 

 shell structure described by Miss Mark on A. vera.* Three layers 

 are present: an inner lamellose layer on which the coarse con- 

 centric ridges which characterize the species are absent or only faintly 

 visible; an outer layer marked by eight to ten elevated ridges separated 



'Meek, F. B., Pal. Ohio, Vol. II, p. 340, 1875. 

 2 Girty, G. H., U. S. Geol. Surv., Bull. 544, p. 144, 1915. 



3 Mark, C. G., Geol. Surv. Ohio, Fourth Ser., Bull. 17, p. 311, PI. XV, Figs, 13, 14, 

 1912. 



