24 



quadrate, upper edge of the outer lip projecting far over 

 the lower. 



Diameter '60 ; height *48 of an inch. 



Locality. — Bloomington ; Spergen Hill. 



\/ Pleurotomaria Swallov ana.— Shell depressed, somewhat 

 globose, spire little elevated ; volutions about five, regularly 

 rounded, the last one sub-ventricose, and sometimes a little 

 more expanded at the periphery ; suture well defined ; aper- 

 ture sub-circular, a little oblique on the pillar ; umbilicus 

 large, circular ; a flattened band upon the periphery of 

 the shell margined on each side by a distinct elevated line ; 

 volutions crossed by fine, even, thread-like striae which 

 are smaller than the spaces between them, more conspicu- 

 ous on the upper side of the volutions and often obsolete on 

 the lower side. 



Diameter *12 to '25; height *07 to '20 of an inch. 



Locality. — Spergen Hill and Bloomington, la. 



Pleurotomaria concava. — Shell trohiform ; spire de- 

 pressed-conical ; volutions about five, flattened or slightly 

 concave above ; base of shell concave ; periphery alate, ala- 

 tion curving downwards at the margin ; aperture transverse- 

 ly ovate (the wider part at the pillar) ; umbilicus medium 

 size, round ; suture linear, rather indistinct ; surface smooth 

 or marked by obsolescant striae, which turn abruptly back- 

 wards from the suture to the periphery ; similar striae are 

 sometimes visible on the base of the shell, bending abruptly 

 backwards on the alation. ' 



Diameter *25 to '75 of an inch ; height from '20 to near 

 *50 of an inch. 



Locality. — Spergen Hill and Bloomington, la. 



v ' Pleurotomaria Leavenworthana.— Shell ranging in form 

 from sub-globose to terate-conical and elongate-ovate ; spire 

 conical, varying greatly in its elevation from the young to 



