INVERTEBRATES. 361 



flattened, the others convex, and provided with a distinct, 

 rather sharp, apparently smooth carina, which occupies a posi- 

 tion a little above the middle of the body whorl, passes around 

 near the middle of the second, becomes lower on the third, and 

 sinks below the suture on the others. Below this angle there 

 is on the body volution a second less distinct subangular promi- 

 nence, with a broad, vertical, nearly flattened or slightly con- 

 cave space between the two. Under side of last turn a little 

 convex; umbilical region somewhatindented, but not perforated; 

 suture well defined. Spiral band narrow, and occupying the 

 principal angle of the whorls. Length, 2 inches; breadth, 

 1.83 inches; apical angle convex, divergence, 70°. 



Our specimen is somewhat eroded, but it retains traces of about twenty 

 ratber strong revolving lines, eight or nine of which occupy the upper side of 

 the whorls, above the carina, some three or four the flattened outer side of the 

 body whorl, and the remainder the under side. On the upper sloping surface 

 of the whorls there are also regularly arranged, oblique transverse striae, which, 

 in well-preserved specimens, are probably continued upon the outer and under 

 sides of the last turn. 



This fine species might be confounded, on a hasty examination, with 

 P. tabulata of Conrad, with which it agrees in size and some other respects. 

 It differs, however, in having the upper part of the spire much more depressed, 

 and without any angle visible above the suture. The principal angle on its 

 other turns appears to differ in being less prominent, and destitute of the crenu- 

 lations so distinctly seen on that of P. tabulata. In addition to these differences, 

 the substance of the shell under consideration is much thicker than in that 

 described by Mr. Conrad. 



Locality and position : Hodge's creek, Macoupin county, Illinois; Lower Coal 

 Measures. 



Pleurotomaria? tumida, M. and W. 



PI. 31, fig. la, 16. 



Platyostoma? tumida, Meek and Worthen, October, 1860. Proceed. Acad. Nat. Sci,, 

 Philad., p. 463. 



Shell rather large, very thin, rhombic subovate in outline, 

 a little longer than wide ; spire much depressed or nearly flat; 



—46 Sept. 26, 1866. 



