110 Trans. Acad. Sci. of St. Louis. 



other authentic specimen is there preserved and here illus- 

 trated. In their description the authors of the species give 

 the diameter of the largest specimen as 15^- mm., but the 

 specimen here illustrated is somewhat smaller, being but 11 

 mm. in maximum diameter. The species may be easily dis- 

 tinguished from its associates by its perfectly flat or even 

 slightly depressed spire. 



Straparollus angularis n. sp. 



PL VI. f. 13-14. 



Shell of medium size with four volutions ; spire not greatly 

 elevated above the outer volution, the suture located in an 

 angular groove. The top of each volution flat or sloping 

 inward, the outer side rounded, meeting the flattened upper 

 side in an obtuse angle so that the shell is marked with a con- 

 spicuous, angular, revolving ridge, and the successive volu- 

 tions form a series of steps from the outer one to the summit 

 of the spire. The surface of the shell marked by somewhat 

 irregular lines of growth which curve gently forward on the 

 outer side of the last volution. Greatest diameter of the 

 shell, 21 mm. 



Remarks. The specimen here illustrated is a plaster cast 

 taken from a natural mould in the sandstone. The under 

 side of the shell is not known but it is probably umbilicate. 

 The specimen bears the name 8. obtusus in the University 

 of Michigan collection, but it is certainly distinct from that 

 species which has a discoid shell with little or no elevation of 

 the spire above the outer volution. The species is quite dis- 

 tinct from any of its associates and seems to be as yet unde- 

 scribed. It most closely resembles 8. luxus White, described 

 from near the base of the Carboniferous strata in Utah, but 

 it differs from that species in having a somewhat higher 

 spire. It also resembles 8. planodorsatus M. and W., from 

 the Kaskaskia beds in Southern Illinois and Missouri. 



Platyschisma barrisi (Win.). 



PI. VI. f. 15-16. 



Straparollus barrisi. Bull. U. S. G. S. No. 153: 604. 

 Shell of medium size, depressed conical in form, with a 

 medium sized, rather deep umbilicus ; volutions four or five 



