INVERTEBRATES. 357 



A revolving line occupying the middle of the spiral band, is 

 more prominent than the others, and obscurely crenulated. 

 Length, 0.17 inch; breadth, 0.15; apical angle regular, diver- 

 gence 60°. 



The interrupted or granulose appearance of the striae on the upper sloping 

 side of the whorls in this little shell, will readily distinguish it from any other- 

 wise similar species with which we are acquainted, in our rocks. In form and 

 general appearance it resembles some of the species described by Prof, de Kon- 

 inck and others in foreign works, but it differs in the details of its surface 

 ornaments. 



Locality and position : Macoupin county, Illinois ; Lower Coal Measures. 



Pleurotomaria Pratteni, M. and W. 



PI. 28, fig. 7a, lb, 1c, Id. 



Pleurotomaria Pratteni, Meek and Worthen, October, 1860. Proceed. Acad. Nat. Sci., 

 Philad., p. 459. 



Shell very small, conical-ovate, the breadth being about 

 two-thirds the length ; spire rather elevated, but not acute at 

 the apex ; volutions six to six and a-half, slightly convex, in- 

 creasing gradually in size, those of the spire more or less dis- 

 tinctly angular around the middle, last one sometimes slightly 

 flattened around the most prominent part of the middle, just 

 below the indistinct angle, and convex on the under side; 

 suture well defined; spiral band of moderate breadth, flat, or 

 sometimes slightly concave, occupying the middle of the body 

 whorl, and passing around so as to bring its lower margin a 

 little above the suture on the other turns. Aperture subcir- 

 cular; columella imperforate; outer lip thin, sinus deep and 

 comparatively narrow. Surface ornamented by about eighteen 

 to twenty very fine revolving striae, some twelve or thirteen of 

 which occupy the body whorl below the band, where they are 

 a little larger than those above the angle, and more regularly 

 arranged; lines of growth extremely minute and obscure. 



