664 



GEOLOGY OF OHIO. 



finer character of the anterior surface markings. Other differences may 

 be noticed in comparing the figures on plate 55. 



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

 Clarksville and Waynesville, Ohio. 



Cyma'onota constricta, n. sp. 



Plate 55. Figs. 10 and 11. 



Shell strongly convex, elongate, the length equaling about three and 

 one-fourth times the greatest height. Dorsal and ventral margin nearly 

 parallel, diverging very sligHtly posteriorly; dorsal margin straight, ven- 

 tral margin gently convex in the posterior half, and slightly concave in the 

 anterior half; anterior end somewhat blunt, its outline almost uniformly 

 rounded; posterior margin slightly oblique, gently rounded, subangular 

 where it joins the dorsal line, sharply rounded and most prominent 

 below. Umbones rather large though distinctly impressed by the mes- 

 ial sulcus; the latter is deeper than in any other species of the genus 

 known and causes the constriction of the shell in a dorsal or ventral 

 view that has suggested the specific name. Umbonal ridge well de- 

 veloped and subangular near the beaks, obscure in the posterior half of 

 the valves. Anterior and posterior gape of valves larger than usual. 

 External surface marked by rather coarse irregular concentric lines of 

 growth, of which only the stronger ones pass through the shell so as to 

 be visible on casts of the interior. Oblique dorsal furrows not sharply 

 distinguished from the lines of growth. In casts of the interior two 

 obscure sulci, one in the middle of the cardinal slope, the other close to 

 the hinge border, may be observed. Hinge and muscular impressions 

 unknown. 



This species is quite distinct from all the others referred to the 

 genus. It might be compared with C. typicalis when it will be" found to 

 differ in its more obtuse anterior end, deeper mesial sulcus, and wider 

 posterior end. 



Formation and Locality. — In the lower part of the upper beds of the 

 Cincinnati group, Butler county, Ohio, and Versailles, Indiana. 



Cymatonota attenuata, n. sp. 



Plate 55. Figs. l->-14. 



Shell strongly convex, gaping at the ends, elongate, highest at the 

 beaks, gradually tapering posteriorly, the length at least four times the 

 height; dorsal margin gently arcuate, declining posteriorly; anterior end 

 neatly rounded, ventral margin almost straight, normally, apparently a 

 little concave; posterior end narrowly rounded, above passing rather 



