is a more distinct suture line. From the latter it differs in its 

 much greater size, in its greater breadth in proportion to its 

 elevation, and in the volution being less angular above the cen- 

 tre, and in having a wide flattened space on the peripery, in- 

 stead of the narrow carina of that species. 



Geological Formation and Locality. In the Buff limestone, 

 of the age of the Trenton limestone group of New York. 



PLEUROTOMARIA nasonj, (n. s.) 



.Description. Shell very depressed conical, the elevation of f 

 the spire being little more than half as great as the breadth 

 across the base, consisting of four or five volutions, which in- 

 crease very gradually from the apex. The upper side of the 

 inner volutions somewhat rounded, becoming more flattened in 

 the outer ones, with a distinct depression near the outer angle 

 which in some specimens extends a little more than half way 

 from the edge of the suture. Under side obtusely rounded in- 

 to the umbilicus, which (in casts) is large and shows about 

 one-third the width of each of the preceding volutions. 



Surface characters unknown. 



This species is somewhat related to P. lenticularis of the 

 Trenton limestone of New York, but the spire is much more 

 elevated, the volutions more distinct and more elevated one 

 above the other, and the lower side is more ventricose, giving 

 a wider periphery. 



Geological Formation and Locality. In the " Buff limestone*' 

 of the age of the Trenton limestone of New York, at Beloit, 

 Wisconsin. 



Collectors. Prof. Nason. and Mr. Hobarl of Beloit, and 

 James Hall. 



PLEUROTOMARIA halei, (n. s.) 



Description. Shell depressed, orbicular, the spire moderate- 

 ly ascending, the hight equal to a little more than two-thirds 

 the greatest diameter, consisting of three or four volutions, 

 which are somewhat rounded on the top, and expanding some- 

 what rapidly in size, the last one quite ventricose, and in the 

 cast is sub-angular on the periphery. The under side of the 

 last volution is rounded from the edge into the rather large 

 umbilicus. 



The surface, as preserved in a mould of the exterior in the 

 stone, is marked on the upper side of the volution by ten or 



