GASTEROPODS. 159 



die of the whorls below. The latter, as shown in young speci- 

 mens, is often well defined, bat after the shell has become half 

 grown, the obtuse prominence becomes obscured. In some 

 specimens the ridge above the periphery is so pronounced as 

 to leave a narrow concave area immediately beneath. 



Horizon and localities. Lower Carboniferous, Burlington 

 limestone: Springfield ( Greene county), Ash Grove ( Greene 

 county), Osceola (St. Glair county ), Louisiana, Hannibal. 



Straparollns latus is the most characteristic form of the 

 genus occurring in the Burlington, but it is not very common. 

 It attains a maximum diameter of eight centimeters. 



Straparollus spergenensis (HALL). 



Euomphalus spergenensis Hall, 1858 : Trans. Albany Inst., vol. IV, p. 19. 



Euomphalus spergenensis, var. planorbifomnis Hall, 1858 : Trans. Albany Inst., 

 vol. IV, p. 20. 



Straparollus spergenensis Miller, 1877: Cat. Am. Pal. Foss, p. 163. 



Straparollus spergenensis var. planorbiformis Miller, 1877: Cat. Am. Pal. 

 Foss., p. 163. 



Euomphalus spergenensis Whitfield, 1882 : Bui. Am. Mus. Nat. Hist , vol. 

 I, p. 69, pi. viii, figs. 16-19. 



Euomphalus spergenensis, var. planorbiformis WhitfieJd, 1882: Bui. Am. Mus. 

 Nat. Hist., vol. I, p. 70, pi. viii, figs. 20-21. 



Euomphalus spergenensis Hall, 1883: Geol. Sur. Indiana, 12th Ann. Kept., 

 p. 350, pi. xxxi, figs. 16-19. 



Euomphalus spergenensis, var. planorbiformis Hall, 1883: Geol. Sur. Indi- 

 ana, 12th Ann. Kept., p. 351, pi. xxxi, figs. 20 22. 



Shell small, depressed conical, composed of four to six 

 rounded volutions, which are more or less flattened above, 

 near the suture; broadly umbilicated; suture well defined. 

 Aperture oblique, circular; lip sharp. Surface marked only by 

 numerous, closely arranged, fine lines of growth. 



Horizon and localities. Lower Carboniferous, Saint Louis 

 limestone : Saint Louis. 



Considerable variation in shape is observable among the 

 shells of this species. Many show quite a marked flattening 

 of the apical portions, while others have the spire more or less 

 elevated, and in this respect closely simulating the type of the 

 genus 8. dionysii Montfort. 



