260 PALEONTOLOGY OF ILLINOIS. 



GASTEROPODA. 



Genus PLEUROTOMARIA, Defrance, 1826. 



(Diet. Sci. Nat., vol. xli, p. 381.) 



Pleurotomaria Shumardi, M. and W. 



PI. 18, fig. 60, 6 5. 



Pleurotomaria Shumardi, Meek and Worthen, Oct., 1860. Proceed. Acad. Nat. Sci,, 

 Philad., p. 462. 



Shell trochiform, of medium size, very thin ; spire moder- 

 ately elevated, conical, # somewhat attenuate at the apex. 

 Volutions about seven, increasing rather rapidly in size, 

 obliquely flattened above; those of the spire somewhat angu- 

 lar near the lower side ; last one very prominent, and angular 

 around the middle, moderately convex below, the immediate 

 edge of the angle being truncated by the narrow spiral band. 

 Band flat or slightly concave, and margined above and below 

 by a small, smooth, slightly elevated line; passing around a 

 little above the suture on the whorls of the spire. Suture well 

 defined; umbilicus small; aperture rhombic-subquadrate, wider 

 than high. Surface ornamented by numerous transverse lines, 

 which are very regular and closely arranged on the upper 

 whorls, but become stronger, more distant and less regular, on 

 the last turn. In crossing the upper, flattened, sloping sides 

 of the whorls, these lines arch a little forward, and pass very 

 obliquely backwards from the suture to the band; on the under 

 side of the body whorl, they are smaller or nearly obsolete, and 

 crossed by obscure traces of fine, revolving striae. Length, 

 0.70 inch; breadth, 0.73 inch; apical angle rather distinctly 

 concave; divergence, 0.70°. 



This handsome species is related to P. conica, of Phillips ( Geol. Yorkshire, 

 vol. ii, p. 288, pi. \f>, Jig. 22 — 1836),. but is a smaller shell, and seems never 

 to have had so many whorls. Its volutions are also more flattened, both above 



