366 TWENTIETH REPORT ON THE STATE CABINET. 



Aperture rounded or slightly elongated, and scarcely sub-angular above 



on the inner side. Umbilical cavity rather large, marked by three or 



four revolving bands. 

 Surface strongly striated ; the upper part of each volution marked by 



five or six revolving cariniform striae above the stronger carina upon 



the angle of the outer volution. These are crossed by fine lines of growth, 



which are not always preserved in the fossil. 



Owing to the thickness of the shell, the internal casts do not often 

 preserve more than three or four bands indicating the exterior striae, and 

 the apicial angle is usually less than that of the exterior shell. 



This species has been identified by Prof. Winchell as Pleurotomaria 

 halei; and two specimens, communicated by him under this name, are in 

 all respects identical with the species described by me under the name 

 Pleurotomaria pauper, from which genus it must be separated on account 

 of the exterior character of the shell which has since been discovered. 



Formation and locality. In limestone of the age of the Niagara group, 

 at Racine, Wisconsin, and Bridgeport, Illinois. 



MURCHISONIA LAPHAMI. 

 PLATE 16 (G),riG. 20 



Murchisonia laphami : Hall, Geological Survey of Wisconsin, Report of Progress, 

 p. 36, 1861, 



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 volutions very slightly flattened, giving a perceptible 

 angularity in the region of the revolving band. Section of volution 

 broadly ovate, the breadth equal to four-fifths of the height, and the 

 greatest diameter on the lower third. 



Surface marked near the middle of the volution by a somewhat broad 

 band, the margins of which are prominent; the upper part of the volu- 

 tions are marked by fine transverse striae, which are directed gently 

 backwards from the suture to the revolving band. 

 This species very closely resembles specimens of the M. logani of the 



Guelph limestone of Canada West, but the volutions of that species are 



more ventricose, and the spire more rapidly ascending. 



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



at Racine, Wisconsin. 



