688 GEOLOGY OP OHIO. 



Externally this species is very much like C. milleri, yet when care- 

 fully compared, several constant differences may be observed. Thus, the 

 ends in that species are relatively narrower, and the cardinal margin slopes 

 regularly down in both directions from the beaks. This is not the case 

 in C. ovata, in which the dorsal outline is slightly sinuate on each side 

 between the point of the beak and the two extremities of the hinge. Fi- 

 nally, the surface markingSxare more delicate in the present form. In- 

 ternally the rudimentary character of the upper and lower pairs of the 

 lateral teeth in the right valve of C. milleri is a sufficient differentation 

 to constitute a specific variation. The oval instead of subcircular outline 

 distinguishes the new, species from C. mediocardinalis. In all other re- 

 spects however the two sptcies are exceedingly close. 



Forntation and, Locality: I,ower beds of the Cincinnati group, at 

 several localities in the vicinity of Cincinnati, Ohio. The horizon is 

 about 100 feet above the bed of the Ohio river at Cincinnati. 



Family PHOLADEIvLID^S, Miller. 



Genus, RHYTIMYA, Ulrich. 



[Pinal Rep. Geol. Sur. Minn., Vol. iii. (In press.)] 



Rhytimya producla, n. sp. 



Plate 56. Figs. 6-9. 



Shell rarely exceeding 39 mm, in length, tapering slightly and ex- 

 tended posteriorly, constricted beneath the moderately prominent urn- 

 i bones; sulcus somewhat oblique, anterior part of shell slightly inflated ; 

 length equaling two and one half times the height at the beaks and three 

 times the height of the posterior third. Cardinal outline very gently 

 concave posterior to the beaks, nearly straight but sloping down about 

 one-third of the height in front of them; anterior margin subrectangular 

 in the middle, then curving gradually backward into the basal line ; pos- 

 terior margin narrowly though rather regularly rounded; ventral margin 

 distinctly sinuate centrally or a little in advance of the center. I^uuule 

 very narrow. Surface marked concentrically, with ten or more sharp 

 regular folds anterior to the beaks and less distinct as well as less regular 

 wrinkles and striae posterior to them. On the compressed post-cardinal 

 region the surface markings are very obscure. The best specimens seen 

 are casts of the interior and on only one of the molds of the exterior are 

 any traces of the radiating series of minute granules perserved. 



Formation and Locality: Middle beds of the Cincinnati group, about 

 325 feet above the bed of the Ohio river at Cincinnati, Ohio, and Coving- 

 ton, Kentucky. Not an uncommon fossil, but good specimens must be 

 considered as rare. 



