382 PALEONTOLOGY OF ILLINOIS. 



Genus TURRITELLA, Lamarck, 1799. 



(Prodr., p. 74.) 



Turritella? ? Stevensana, M. and W. 



PL 21, fig. 8 and 8 a. 



Shell very small, elongate, slender, and very gradually taper- 

 ing to a pointed apex; volutions ten to twelve, distinctly convex, 

 and rather rounded, increasing gradually in size, last one form- 

 ing about one-fourth the entire length — all very slightly flat- 

 tened just below the suture, the flattened space being narrow 

 and sloping outwards; suture well defined in consequence of 

 the convexity of the whorls. Surface ornamented by small, 

 prominent, thread-like, revolving lines or costse, separated by 

 impressed spaces about three times their own breadth ; of these 

 costse, five or six may be counted on the body whorl, and four 

 or five on each of those of the spire. Crossing all the costse 

 and spaces between, there may also be seen, by the aid of a 

 magnifier, numerous minute, strongly sigmoid lines of growth. 

 Aperture unknown. Length, 0.27 inch; breadth, 0.09 inch; 

 apical angle very regular, divergence about 20°. 



We only know this little shell from moulds left in the matrix, and our figures 

 were drawn from wax casts made in one of these moulds, which, however, are 

 so sharply defined as to show clearly the most minute surface markings. Judging 

 from the form of the last whorl, it is probable the aperture is nearly circular, 

 and the lines of growth indicate that the outer lip must be broadly retreating, 

 near or a little above the middle (without, however, having any traces of a 

 defined sinus), and very prominent below. The moulds also show that the 

 under side of the last whorl is marked by small, rather crowded, revolving lines, 

 considerably less than those above, and indicate that the columella was probably 

 not perforated. 



It is with great reluctance that we refer this little shell, even provisionally, 

 to the genus Turritella, since we have good reasons for believing that that genus 

 was not introduced until long after the Carboniferous period. As it seems, 

 however, not to belong to any of the known palaeozoic genera, and is more like 



