178 Natural History Bulletin. 



by its more elevated spire, lax volutions, wider umbilicus and 

 consequently greater difference in the lateral sweep of the suc- 

 cessive volutions. 



Found in Niagara limestone at Monmouth, Iowa, associated 

 with Pentamerus oblongtis, Straparolltis bicarinatus^ etc. 



Height of specimen containing three large volutions, two 

 and a half inches; width of base, measured from side to side 

 at right angles to axis, two and a half inches. 



STR APAROLLUS, Montfort. 

 EuOMPHALUS, Sozucrby. 



ECCYLIOMPHALUS, Portlock. 



Phanerotinus, Sozucrby. 

 Straparollus lativolvis, n. s. 



PLATE I., FIG. I, AND PLATE II., FIG. I. 



Shell very large, discoid, planorbicular; spire depressed 

 below the level of the outer volutions; whorls few, not more 

 than three, the casts rarely preserving more than one and a 

 half; whorls rapidly enlarging from the apex, the outer one in 

 large specimens attaining a diameter of more than two and a 

 half inches. The contiguous volutions are scarcely in contact, 

 and lie so nearly in the same plane as to make, the spire and 

 umbilical sides very much alike. Volutions slightly flattened 

 above, more regularly rounded below. Aperture transversely 

 elliptical. No carinas. 



From casts in the matrix it is seen that the surface was 

 ornamented by regular, rather coarse stride transverse to the 

 whorls and parallel to the lines of growth. 



This shell is known from natural casts of the interior and 

 impressions of the external surface in the original matrix. 

 The species is one of the largest of the genus, one of the spec- 

 imens having a maximum diameter of six and one-fourth 

 inches. 



Found abundantly in limestone usually referred to the age 

 of the Hamilton group of New York in Newton township, 



