THE LOWER SILURIAN ROCKS. 665 



gradually into the dorsal margin. Beaks small, compressed; mesial 

 sulcus and umbonal ridge but little developed. Surface marked by con- 

 centric lines of growth, very fine, crowded and subequal on the anterior 

 third, fewer and coarser on the central and posterior parts, and obscure 

 on the umbonal ridge; oblique dorsal folds strong and regular. 



The tapering character or the posterior end will distinguish this 

 peculiar species from all the others now referred to the genus Cyma- 

 tonota. 



Formation and Locality. — Upper beds of the Cincinnati group, 

 Waynesville, Ohio. 



Cymatonota productifrons, n. sp. 



Plate 55. Figs. 17 and 18. 



Shell ventricose in the posterior half, only moderately elongate, the 

 length about three times the greatest height. Beaks small, situated 

 more than one-third of the length of the shell behind the anterior ex- 

 tremity. Anterior end very long, tapering slightly, the outline some- 

 what sharply rounded above; hinge line nearly straight, but little 

 shorter than the greatest length of the shell; posterior end one-third 

 wider than the anterior, the margin rounded; basal line nearly straight 

 in the central half, curving upward strongly at each end. Mesial sulcus 

 and umbonal ridges scarcely defined. Surface marked with concentric 

 lines of growth. These are distinct and regular on the sides of the 

 valves and comparatively obscure on the ends. Dorsal furrows strong 

 and regular for two-thirds of the length of the hinge posterior to the 

 beaks, under a good glass exhibiting exceedingly fine lines of growth. 



This shell, though appearing to agree in all other respects with the 

 genus Cymatonota, differs very conspicuously from the other species in 

 its greatly produced anterior end. 



Formation and Locality. — Only two specimens have been seen of this 

 species, and these were both collected in the lower shales of the Cincin- 

 nati group at Covington, Kentucky. The horizon is about 100 feet 

 above the bed of the Ohio river. 



Genus PSILOCONCHA Ulrich. 



[ Final Rep. Geol. Sur. Minn. vol. iii, p. 530 (in press).] 



Psiloconcha grandis, n. sp. 



Plate 52. Figs. 1 and 2. 



' Shell large for the genus, compressed convex, highest near the mid- 

 dle, the length two and two-fifths times' the height, the thickness less than 

 one-half of the height. Outline elongate subelliptical ; cardinal margin 



