3C2 PALAEONTOLOGY OF ILLINOIS. 



volutions four to four and a-half, convex, increasing very rapidly 

 in size ; last one large, forming about eight-ninths of the entire 

 length, prominent, and narrowly rounded above the middle, 

 slightly convex on top, and contracted and somewhat extended 

 below ; suture well defined ; aperture large, longer than wide, 

 obovate, the inner side being straighter than the other ; lip 

 very thin; columella perforated?; surface (of an exfoliated 

 specimen) retaining traces of rather strong revolving lines. 

 Length, 1.24 inches; breadth, 1.20 inches; length of aperture, 

 1.05 inches; breadth, about 0.65 inch; apical angle regular, 

 divergence, 1.32°. 



We are in much doubt in regard to the generic relations of this shell, not 

 having seen specimens in a condition to enable us to determine whether or not 

 it possessed the spiral band and sinus in the lip, so characteristic of the genus 

 Plcurotumarta. It certainly differs materially from the usual forms of the 

 species of that genus, having more the outline of the recent genus Ianthina. 

 We suspect it will prove to belong to an undescribed genus, which should pro- 

 bably include a Russian form figured by Murchison de Verneiul and Keyser- 

 ling, in the Geology of Russia, pi. xxiii, fig. 14, as an undetermined Ianthina. 

 If so, we would propose for the group the name Ianthinopsis, from its resem- 

 blance to the genus Ianthina. 



We cannot believe that Carboniferous shells such as this can be properly 

 referred to the recent genus Ianthina, since no species of that genus are known 

 from any of the succeeding rocks, until we ascend to the most recent Tertiary 

 beds; nor can we agree with d'Orbigny in placing them in the Lower Silurian ge- 

 nus Scalitcs, which was founded upon thick shell, with distinctly angular whorls. 



Locality and position : Grayville, Illinois; Upper Coal Measures. 



Genus STRAPAROLLUS, Montfort, 1810. (See page 158.) 



(Conch. Syst., ii, p. 174.) 



Strapakollus umbilicatus, M. and "W. 



PL 29, figs, Iff, 1 J, le. 



Stra/iarollus umbilicatus, Meek and Worthen, Oct., 1860. Proceed. Acad. Nat. Sci., 

 Phila'd., p. 462. 



Shell of medium size, depressed subtrochiform; spire rather 

 elevated for a species of this genus ; volutions five to five and 



