184 TWENTT-FOURTR REPORT ON THE StATE MuSEVM. 



forms, there seems no sufficient reason for recognizing them as dis- 

 tinct species. 



Pentameeus Knappi n. sp. 



Shell broadly elliptical, moderately gibbous above, compressed in 

 front; length about one-third greater than the breadth, somewhat 

 obscurely trilobate ; cardinal line equal to nearly half the width of 

 the shell. Dorsal valve scarcely smaller than the ventral, moder- 

 ately gibbous in the upper part, broadly depressed-convex below the 

 middle, and spreading at the latero-basal margins. Yentral valve a 

 little more gibbous in the middle above than the opposite valve, and 

 less depressed in the lower part ; the beak narrower below, closely 

 incurved, and extending a little beyond that of the opposite valve. 



Surface with strong plications in the middle, which reach only to 

 the umbo, diverging and curving outward below ; they are rounded, 

 and repeatedly bifurcating, with the growth of the shell, so that there 

 are about six times as many on the margin as at their origin ; sides 

 of the shell smooth or free from plications, the limit between the 

 plicate and non-plicate portions indicated by a depression or sinus 

 which gives an indistinct trilobed character to the shell. Marked 

 everywhere by fine concentric striae of growth. 



In the single specimen examined, the ventral valve shows the 

 single longitudinal septum, and the dorsal valve the two thin, gently 

 diverging septa, — in these respects differing in no degree from 

 P. oUongus. 



This fossil recalls to mind at once the StricMandinia Gasjpensis 

 Billings, but it has no sinus or fold in the middle of either valve, 

 and it wants the straight hinge extension and narrow area, as well 

 as the radii on the lateral portions of the shell, which are character- 

 istic of that fossil. 



In every feature, except the strongly radiated surface, this species 

 does not differ from Pentamerus ohlo7igus ; and however unwar- 

 ranted such a suggestion may appear at the present time, it is not 

 improbable, when we compare some of the more extravagant forms 

 already referred to that species, that intermediate ones may be 

 found. 



Formation and locality. In strata of the age of the Niagara group 

 near Louisville, Ky. Cabinet of Dr. James Knapp. 



Pentamekus Xysius n. sp. 



Shell varying with age from broadly triangular with little gib- 

 bosity, to subquadrate from extension of the mesial portion in front 

 with increasing gibbosity; in larger specimens assuming an ovoid 



