3GG PAL2E0NT0L0GY OF ILLINOIS. 



;i neat, symmetrical little species, somewhat resembling Nerita spirata, Sowerby, 

 excepting that its spire is not so much depressed, while the upper side of its 

 whorls arc not flattened. It is proportionally shorter and more ventricose than 

 Naticopsis ventrica—(NaMca ventrica, Norwood and Pratten), from which it 

 also differs in not having its body whorl constricted around the middle. 



We have before us a number of specimens from the Lower Coal Measures on 

 Hodge's creek, Macoupin county, Illinoisffcpresenting almost precisely the same 

 form and general appearance as the species under consideration, but differing 

 in attaining three or four times as large a size, and in having the thickened 

 columella sometimes transversely striated. It is possible the species here 

 described may be identical with these, but we think the specimens alluded to 

 from Hodge's creek, the young of a large ponderous species quite common at the 

 same locality. If so it would seem scarcely possible that the little shell here 

 described, from the Upper Coal Measures, can be the same species. 



In our figure of the species under consideration, the engraver has, by some 

 accident or mistake, carried a ridge around the inner upper side of the aper- 

 ture, which gives it an unnaturally rounded appearance above. 



Locality and jwsition : Upper Coal Measures, Springfield, Illinois. 



Subgenus TRACHYDOMIA, M. and W. (See page 364.) 

 Naticopsis nodosa, M. and W. 



PL 31, fig. 2a, lb. 



Naticopsis nodosa, Meek and Worthen, October, 1860. Proceed. Acad. Nat. Sci., 

 Philad., p. 463. 



Shell rather large, obliquely subrhomboidal in outline, 

 rather thick ; volutions four and a half, convex, increasing 

 rapidly in size, last one large, gibbous, and composing three- 

 fourths of the entire length, rounded on the outer side, and 

 having a shallow revolving depression near the suture above ; 

 suture moderately distinct ; aperture rounded subovate, some- 

 what straightened on the inner side ; lip sharp ; columella 

 distinctly flattened, smooth, and having a small opercular 

 groove near the base, not perforated. Surface ornamented by 

 numerous prominent nodes, which are arranged in quincunx, 

 so as to form oblique rows nearly parallel to the lines of growth, 



