358 PALAEONTOLOGY OF ILLINOIS. 



Length, 0.24 inch; breadth, 0.18 inch; apical angle convex, 

 divergence, 37°. 



The most marked peculiarity of this species is the fineness of its surface 

 markings, particularly the lines of growth, which are scarcely visible even by 

 the aid of a common lens. The revolving striae, although much larger than 

 those crossing them, are not distinctly seen without the use of a magnifier. 

 Generally the carina on the middle of the upper whorls is well defined, but it 

 becomes less distinct on the body volution. The measurements given above 

 are from an adult specimen slightly above the medium size. 



The specific name of this beautiful little shell was given in honor of our 

 lamented friend, Henry Pratten, Esq., deceased, formerly of the Illinois Geo- 

 logical Survey. 



Locality and position: Same as last. 



Pleurotomaria subsinuata, M. and W. 



PL 28, figs. 4a, 46, 4c, 4d. 



Pleurotomaria subsinuata, Meek and Woethen, Oct., 1860. Proceed. Acad. Nat. Sci., 

 Philad., p. 460. 



Shell under medium size, conical-ovate; spire rather ele- 

 vated; volutions six, convex, last one in mature shells some- 

 times obliquely flattened a little above, just below the suture, 

 thence rounded below; suture well defined ; spiral band narrow, 

 prominent, angular, located above the middle of the body whorl, 

 at the lower edge of the slight flattening of its upper side, and 

 passing around the middle of the upper turns; sinus of the lip 

 shallow, judging from the slight curve of the lines of growth ; 

 aperture nearly circular ; columella not distinctly perforated. 

 Surface ornamented by about fifteen distinct revolving lines, 

 some three or four of which on the middle are larger than those 

 above, while those below gradually diminish in size towards 

 the small umbilical impression; only two or three of the smaller 

 lines usually occupy the slightly depressed portion of the 

 whorls above the spiral band, where they are crossed obliquely 

 by a series of regularly arranged wrinkles ; lines of growth ex- 



