25 



the old shell ; volutions five to seven, neatly rounded and 

 ventricose below ; suture well defined ; aperture round- 

 oval ; umbilicus none ; surface marked by conspicuous, 

 rounded, revolving stria3, which are less than the spaces 

 between ; stria? less conspicuous on the base of the last vo- 

 lution ; the first line below the suture uniformly thinner 

 and sharper than the others, and the spaces on each side 

 wider. 



Length from *05 to *50 of an inch. 



Locality. — Spergen Hill ; Bloomington, la. ; Alton, 111. 



^Pleurotomaria trilineata. — Shell ovate-conical; spire 

 more or less elevated, acute at the apex ; volutions about 

 six, convex, last volution ventricose ; suture distinctly de- 

 fined ; aperture sub-circular ; columella perforate by a small 

 umbilicus ; surface marked upon the periphery by a com- 

 paratively broad spiral band, which is margined on each 

 side by a linear groove ; two other similar grooves between 

 the band and the umbilicus, dividing the base of the shell 

 into three spaces, each one equaling in width the spiral 

 band ; entire surface, except the spiral band, ornamented 

 by revolving, thread-like stria?, which are crossed by fine 

 lines of growth, the latter becoming stronger and curving 

 slightly backward upon the spiral band ; an almost imper- 

 ceptible angulation just below the umbilicus. 



Length *125 to '50 of an inch. 



Locality. — Spergen Hill ; Bloomington, la. 



Pleurotomaria subanglata. — Shell ovate-conical ; volu- 

 tions about five or six, angular above, the last one ventri- 

 cose below ; upper side of volution nearly rectangular to 

 the direction of the spire ; aperture ovate, the inner side 

 straight or concave ; umbilicus none ; suture distinct ; sur- 

 face ornamented by unequal, revolving lines, those on the 

 lower part of the last volution finer and more closely ar- 

 ranged, three of those on the periphery stronger and more 

 distant, the upper one of these three stronger than the other 



[Trans, iv.] 5 



