36 



Surface finely striated on the lower side of the volution, 

 with a deep retial curve on the band, where the strise are 

 somewhat fasciculate. 



This species resembles P. umbilicata of the Trenton lime- 

 stone, but the volutions are more elevated above each other, 

 and the upper surface is wide and flat. 



Geological Formation and Locality. In limestone of the Ni- 

 agara group, at Racine, Wisconsin. 



Collector. T. J. Hale. 



PLEUROTOMARIA sbmele, (n. s.) 



Description. Shell sub-conical; spire ascending; hight and 

 breadth nearly equal, consisting of four or five rounded or 

 sub-angular volutions, the last one ventricose, sub-angular on 

 the periphery, regularly rounded below with the small umbili- 

 cus. Aperture round. 



Surface marked by a sub-angular carina a little below the 

 suture, and on the periphery by a moderately broad revolving 

 band, sharply elevated at the margins and concave in the 

 middle. Entire surface marked by sharp, elevated, closely 

 arranged, concentric stride, which are curved abruptly back- 

 wards from the suture to the revolving band, on which they 

 make a shallow retral curve, and below the band, have a gentle 

 forward curvature in passing downward to the umbilicus. 

 Hight a little more than one inch ; width three-fourths of an 

 inch. 



This species differs from any other known in rocks of the 

 lower Silurian rocks, in the form of the volutions and surface 

 markings. 



It may be that this is a murchisonia, the elevation of the 

 spire being greater than the width of the shell : but the aper- 

 ture is too imperfect to determine it. 



Geological Formation and Locality. In the shales above the 

 Galena limestone, at Makoqueta creek. 



GENUS MURCHISONIA, Phillips. 



MUROHISONIA laphami, (n. s.) 



Description. Shell turritiform, robust; volutions seven or 

 eight, gradually increasing from the apex, rather ventricose 

 on the exterior, with close sutures; the upper half of the 

 volution very slightly flattened, giving a scarcely perceptible 

 angularity in the region of the revolving band. Section of 

 volution broadly ovate, the breadth equal to four-fifths of the 

 hight, and the greatest diameter on the lower third. 



