INVERTEBRATES. 359 



tremely fine and very obscure. Length of largest specimen, 

 0.40 inch ; breadth, 0.31 inch ; apical angle convex, diver- 

 gence, 55°. 



The spiral band of this species is so little apparent that we were at first in 

 .doubt whether it really belongs to the genus Pleurotomaria. On examining 

 carefully, however, by the aid of a lens, the obscure lines of growth, we observe 

 that they make a small but distinct backward curve in crossing the upper of 

 the three or four larger revolving lines passing around the middle of the body 

 whorl, so as to indicate the presence of a shallow sinus in the lip at the termi- 

 nation of this revolving line. The band of the sinus being angular or carinated, 

 and scarcely larger than the other revolving lines, would not be distinguished 

 from them, where the surface has been a little weathered so as to obliterate the 

 obscure striae of growth. 



The surface markings will at once distinguish this shell from any of its asso- 

 ciates, and we know of no foreign forms with which it is liable to be confounded. 



Locality and position: Same as preceding. 



Pleurotomaria turbiniformis, M. and W. 



PI. 28, fig. 8 a, 8 5, 8 c. 



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



Philad., p. 461. 

 Pleurotomaria bicarinala, McChesney, Feb., 1860. New Palaeozoic Fossils, p. 90; (not 



P. bicarinata, Sowerby, sp., 1818, de Koninck, 1843, nor of Munster, 1844). 



Shell rather large, trochiform ; height and breadth nearly 

 equal; spire conical, moderately depressed; volutions about five 

 and a half, flat, last one distinctly angular around the periphery, 

 and flattened or slightly convex below; umbilical region a 

 little concave; umbilicus very small, and bound by a small, 

 obscure, revolving ridge; spiral band extremely narrow, 

 grooved, occupying the angle around periphery of the body 

 whorl, and passing around scarcely above the suture on the 

 other volutions, margined above and below by a sharply eleva- 

 ted line; suture linear, having a somewhat banded appearance 

 in consequence of the development of a rather distinct revolv- 

 ing line at the upper margin of each whorl ; aperture appa- 



