$0 PALEONTOLOGY OF KENTUCKY. 



Pentamerus nysius, var. crassicostus. HALL. 



Plate XXVIII., figures 5, 6, 7 and 8. 



Pentamerus nysius, var. crassicostus, Hall. 24th Kep. N. T. State Mus., p. 184. 

 Pent, nysius, var. orassicostus, Hall. 27th Kep. N. Y. St. Mus., pi. 10, figs. 4 and 71875. 



Shell large, at least above the medium size ; sub- triangular or sub-quadrate, 

 sometimes becoming obscurely trilobate ; length always, or mostly, exceeding 

 the width. Ventral valve gibbous ; greatest convexity below the umbo, from 

 where it curves gently to the front, and, at first slightly and later abruptly, to 

 the lateral margins from apex to the front. This abruptly bent portion of the 

 shell is always smooth. The beak is strong and pointed, and arched over a 

 large open fissure ; it is considerably elevated over the umbo of the other 

 valve. This valve has its surface divided, by two prominent concentric lines of 

 growth, into three zones, all of which are, however, covered by the radii. On 

 some of the shells belonging to this species these zones are not noticeable. The 

 dorsal valve is less convex than the other, it is depressed convex, with its 

 maximum convexity at the umbo, from where it slopes in a gentle curve to the 

 anterior and lateral margins. A strip on its lateral margins is abruptly bent 

 towards the ventral valve, and is not covered by radii ; the umbo is regularly 

 curved and reaching into the fissure of the opposite valve. 



The surface is covered by single, strong and rounded plications, numbering 

 from twenty to twenty-five. 



Formation and Locality. Occurs somewhat abundantly in the Niagara rocks in the quarries east 

 of the city of Louisville, Ky.; but well preserved specimens are rather rare. In my own cabinet there are 

 some very perfect specimens of this species. 



Pentamerus nysius, var. tenuicostus. HALL. 



This variety agrees in every essential point with the preceding one, with the 

 exception of the radii. These are strong and coarse in the latter, and fine and 

 more numerous in the present variety. The number of costae never exceeds 

 twenty-five in P. crassicostus, while in P. tenuicostus it is about forty. 



Formation and Locality. Found associated with the preceding variety in the Niagara rocks easl 

 of the city of Louisville, Ky. ; somewhat rarer than the former. 



Pentamerus oblongus. SO-WERBY. 



Plate XXXIII., figures 16, 16 and 17. 

 Pent, oblongus, Sowerby. Murch. Sil. Syst., p. 641 1839. 

 Pent, laems, Ibrid. Iden, pi. 19, fig. 9. 



Pent, oblongus, Hall. Geol. Rep. of 4th Dist. N. Y., p. 71843. 

 Pent, oblongus, Hall. Pal. N. Y., Vol. II., p. 79, pis. 25 and 26. 



Shell sometimes very large, but very variable in size and form. It would be 



