FOSSILS OF THE SILURIAN AND DEVONIAN ROCKS. 211 



smaller one considerably. In this shell the width is only about three-fourths 

 of the length. It is covered with strong concentric striae, which are sharply 

 marked, almost all parallel to each other and equidistant. The depression of 

 its dorsal margin in front of the beaks is very conspicuous ; the illustration 

 does not show this at all, or very faintly. The beaks are close to the anterior 

 margin ; the anterior slope is steep, while the posterior one has only little fall. 

 The size of this shell varies in different specimens ; it agrees generally with 

 that of P. lirata. Both valves are moderately convex. 



It differs from P. lirata by its elongate shape and by the position of its 

 beaks, which is sub-anterior, while the position of the beaks in P. lirata is 

 almost central. 



Formation and Locality. Found in the cherty layers superimposed upon the hydraulic limestone 

 of the Devonian formation, in Jefferson county, Ky., and in Clark county, Ind. It may be possible that 

 some intermediate forms exist which connect this new species with P. lirata; but it appears to me that 

 both species are sufficiently different to guarantee the existence of the new one. 



Paracyclas lirata. CONRAD. 



Plate II., figures 4, 5, 6 and 7. 



Posidonia lirata, Conrad. Geol. Surv. N. Y., Ann. Kep. 1838. 

 Paracyclas lirata, Hall. Pal. N. Y., Vol. 5, pt. 1, p. 441, pi. 72, figs. 2-19. 



Shell of medium size, sub-circular or broadly elliptical ; length a little 

 greater than height; margins regularly rounded. Cardinal lines short, less 

 than half the length of the shell. Valves moderately convex below, becoming 

 gibbous on the middle and above. 



Beaks anterior to the center; small, appressed, rising but little above the 

 hinge-line. Post- cardinal slope not defined. 



Surface marked by fine concentric striae, and by strong, sub-angular, con- 

 centric ridges, which are more or less sharply defined, depending upon the 

 condition of the specimen and the nature of the matrix in which the fossil is 

 imbedded. 



Ligamental grooves distinctly marked and only moderately divergent from 

 the cardinal margin. 



In form this shell is very like the elliptica, but considerably smaller in size, 

 and marked by more or less distinct, angular, concentric ridges. It also re- 

 sembles Lucina lineata of Goldfuss, from the Devonian formation in Germany, 

 with which it may be found specifically identical. (Hall.) 



The size of this species is very variable, as may be seen from the figures on 

 plate 2, which are of natural size. Prof. Meek, in the first volume of the 

 Palaeontology of Ohio, has figured and described a Par. ohioensis, which bears 

 a very close resemblance to Par. lirata, and differs only from the latter by a 



