590 Contributions to Invertebrate Palaeontology. 



considered as an organic feature of the species. A single individual 

 among them shows this feature existing on all of the volutions, the 

 outer whorls reaching to just below the expansion. 



The shell is of a form common to the Lower Carboniferous for- 

 mations, and also to those referred to the Waverly group and to 

 the Chemung of New York ; species occurring both with and 

 without the revolving carinas, E. Hecale Hall (Illust. Dev. Foss., 

 pi. 16, figs. 12), of the Chemung group, is usually destitute of the 

 ridges, as is also S'. cyclosfomus, of the Burlington sandstones of 

 Iowa and other States. There are forms in the Lower Carbonifer- 

 ous of Illinois, in the St. Louis and Chester groups, showing the 

 carinse, as does also Euomphalus (Strap.) laxus White, and Euomph. 

 (Strap. ) Utahensis H. and W., from the Waverly group as represented 

 in the far West. The different species described present slight dif- 

 ferences from each other, but are all so closely allied in form as to 

 be not readily distinguishable. 



Forviation and Locality. — In the Maxville limestone, Chester 

 group, at Newtonville, and near Maxville, Ohio. Collected b}' Prof. 

 Andrews. 



Geuns IVATICOPSIS McCoy. 

 IVaticopsis ziczac. 



Plate XIV, figs. If) and 16. 



Natkopsis ziczac Whitf., Ann. N. Y. Acad. Sci., 1882, p. 223. 



Shell small, the greatest diameter of the body-volution, in the only indi- 

 vidual seen, being about nine-sixteenths of an inch ; and the entire vertical 

 height of the shell only half an inch. The shell is very obliquely ovate in 

 form, and consists of about two and a half ventricose volutions, which increase 

 somewhat rapidly in size to the last one, which forms nearly the entire bulk 

 of the shell. The surface of the shell is ornamented by a series of strong and 

 raised transverse lines, which, on tlie upper volutions, are simple as far as the 

 suture below, and are directed strongly backward in their passage ; but on 

 the body-volution they appear more distant and conspicuous, and are directed 

 strongly backward in their passage for about one-third the vertical diameter 

 of tlie volution, where they are bent forward at an acute angle, and after con- 

 tinuing for a distance nearly equal to their length above, are again bent back- 

 ward. Across the middle of the volution, they make two or more zig-zaggiug 

 bends in vertical lines, forming a revolving band of vertical ridges on the 

 periphery ; below this band, tlie lines are directed forward obliquely, running 

 nearly parallel to the base of the shell. 



The peculiarity of this shell consists entirely in the structure of 

 the surface ornamentation, as the general form of the species is 



