44 Trans. Acad. Sci. of St. Louis. 
This genus is distinguished from all other Ordovician 
Pleurotomaridae by the shallow slit which occurs very 
low on the whorl. It differs from other slit-bearing forms 
in the shape of the shell, resembling Cyclonema in this 
respéct. 
Genus and species based on a single perfect specimen. 
Number 11552 of the invertebrate paleontological collec- 
tion of Walker Museum. 
HELICOTOMA MISSOURIENSIS, Nl. sp. 
Pl. vu. f. 11-12. 
Shell large, diameter twenty-seven millimeters, height. 
fifteen millimeters. Whorls five, the upper two coiled in 
nearly the same plane, the others rising gradually. Upper 
surface of whorls sloping slightly toward the suture line, 
slightly convex in the middle, a decided furrow one-half 
millimeter outside the suture line. Outer surface of lower 
whorl convex below, concave above, outer surface of other 
whorls straight, sloping slightly outward. Lines of 
growth sigmoidal, outer ends curving strongly backward 
to the notch-carina. Notch-carina prominent, umbilicus 
small. 
H. missouriensis agrees with H. tennesseensis save in 
having a furrow one-half millimeter outside the suture 
line and none at the suture line. 
This species is based on a single well-preserved speci- 
men. Number 11528 of the paleontological collection of 
Walker Museum. 
LIOSPIRA, N. sp. 
This species differs from Liospira micula in having a 
smaller apical angle, in having the suture well impressed, 
and in the whorls being slightly convex upward. 
One specimen too imperfect for description is in the 
collection. Number 11549 of the invertebrate paleon- 
tological collection of Walker Museum. 
