44 Trans. Acad. Sci. of St. Louis. 



Tills genus is distinguished from all other Ordoviclan 

 Pleurotomarldae by the shallow silt which occurs very 

 low on the whorl. It differs from other sllt-bearlng forms 

 In the shape of the shell, resembling Cyclonema in this 

 respect. 



Genus and species based on a single perfect specimen. 

 Number 11552 of the invertebrate paleontological collec- 

 tion of Walker Museum. 



HELICOTOMA MISSOURIENSIS, U. Sp. 



PI. vii. f. 11-12. 



Shell large, diameter twenty-seven milhmeters, height 

 fifteen mlHimeters. 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. 



LiospiEA, 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. 



