152 PALAEONTOLOGY OF ILLINOIS. 



Shell small, cylindrical at the upper extremity, and slightly 

 inflated below, giving it when the septate portion is preserved 

 a slightly ovate outline. 



Dorso-ventral diameter a little more than the lateral, and 

 greatest about midway between the two extremities. Septa 

 not preserved but apparently about two. Siphuncle proportion- 

 ately large, septate, and situated close to the dorsal side. 



Length of the best preserved specimen, incomplete at the 

 upper extremity 1% 6 inches; breadth of the dorso-central side 

 about midway of its length 7 / 16 inch; breadth of opposite side 

 6 / 16 inch. 



Position and locality: Niagara limestone, Port Byron, 111. 



Collector, J. H. Southwell. 



No. 2588 of the Illinois State Museum. 



