INVERTEBRATES. 3G3 



a half, convex, increasing gradually in size, nearly horizontally 

 flattened on the upper side, about half way across from the 

 suture, where there is a rather distinct revolving angle ; below 

 this angle the upper oblique outer slope is slightly flattened to 

 near the middle of the outer side, which, in the last whorl, is 

 rather narrowly rounded ; under side of last turn rounded to 

 a moderately distinct angle within the middle, thence rounding 

 into the umbilicus ; umbilicus large, or nearly twice as wide as 

 the diameter of the last whorl near the aperture, very deep, 

 and permitting the inner side of all the volutions to be seen to 

 the summit of the spire. Surface marked by fine, rather 

 obscure or moderately defined lines of growth. Height, 0.88 

 inch; breadth, 1.15 inches; breadth of umbilicus, measuring 

 across from its marginal angle on opposite sides, 0.68 inch; 

 apical angle convex, divergence about 100 °. 



This species is evidently closely allied to Sira/parollus acutus= (Cirrus acutus, 

 Sowerby, Min. Conch., pi. 141, figs. 1 and 2), but has a proportionally wider 

 umbilicus and narrower whorls, while the angle on the under side of its last 

 whorl is farther in, so as to form the margin of the umbilicus. Its lines of 

 growth are also less strongly marked, those of S. acutus, being described by 

 de Koninck as forming even imbricating laminae on the last turn. 



Locality and position : St. Clair county, 111. ; Lower Coal Measures. 



Genus NATICOPSIS, McCoy, 1844. 



(Oarb. Foss. Ireland, p. 33.) 

 Synon. — Natica, of some authors ; (not of Aadanson). 



Shell oval or subglobose, solid, imperforate, composed of 

 few, convex, rapidly expanding whorls, the last one of which 

 is large; spire short; aperture broadly subovate, straighter on 

 the inner side, and rounded below ; columella callous, more 

 or less distinctly flattened, and often showing a longitudinal 

 impression for the reception of the edge of the operculum ; 

 sometimes transversely furrowed or striated; lip sharp and 

 entire. Surface generally nearly smooth on the middle and 



