GASTEROPODS. 135 



periphery, and from twelve to fifteen below ; the spaces be- 

 tween the ridges are shallow and regularly concave from crest 

 to crest; crossing these are numerous fine undulating lines of 

 growth. 



Horizon and localities. Lower Carboniferous, Burling- 

 ton limestone: Hannibal. 



Worthen's original description of this shell was based upon 

 a very imperfect specimen, and was unaccompanied by illus- 

 trations of any kind ; and it was not until more than eight years 

 afterward that suitable figures of the form appeared. Were 

 not the shell such a striking species, so different and so easily 

 distinguished from all other forms of the genus, it would hardly 

 be regarded as unjust to ignore altogether, the name given by 

 Worthen. 



Pleurotomaria subcarbonaria SP. NOV. 



Plate xlix, fig. a. 



Shell small, closely resembling an immature specimen of 

 P. carbonaria. 



Horizon and localities. Lower Carboniferous, Burlington 

 limestone : Louisiana ( Pike county) ; Kinderhook beds : Bur- 

 lington ( Iowa ). 



Pleurotomaria turbiniformis MEEK & WORTHEN. 

 Plate xlvlii, figs 6a-b. 



Pleurotomaria bicarinata McChesney, 1860: New Pal. Foss., p. 90. (Not 



Sowerby, 1818, nor de Koninck, 1843, nor Munster, 1844.) 

 Pleurotomaria turbiniformis Meek & Worthen, 1860: Proc. Acad. Nat. Sci., 



Phila., p. 461. 

 Pleurotomaria turbiniformis Meek & Worthen, 1866: Geol. Sur. Illinois, vol. 



II, p. 359, pi. xxviii, figs. 8a-c. 

 Pleurotomaria turbiniformis White, 1884: Geol. Sur. Indiana, 13th Ann. 



Rep., pt. ii, p. 160, pi. xxxii, figs. 7-8. 



Shell rather above medium size, top-shaped, about as high 

 as wide; spire occupying less than half the height; whorls 

 five to six in number, sharply angular around the periphery, 

 obliquely flattened above, slightly convex below, and curving 

 gently into the small umbilicus ; band very narrow ; aperture 

 obliquely subquadrate ; surface marked by strong transverse 



