590 PALEONTOLOGY OF ILLINOIS. 



by regular, distinct, annular costse, which pass around a 

 little obliquely, and are separated by rounded furrows of 

 the same breadth as the cost*e themselves. 



Length of a specimen incomplete at both ends, 0.28 inch ; 

 diameter at the larger end, 0.06 inch ; do. at smaller end, 

 0.04 inch. 



Of this delicate little shell we have seeii but a single specimen, which 

 is imperfect at both ends. At a first glance it might be mistaken for 

 another more common species, of near the same size, occurring at the 

 same locality, and which we are inclined to think is the I). MeckiaiHtm, 

 of Geinitz. On examii ing it under a magnifier, however, it can be at 

 once distinguished by its comparatively strong, regular costa?, instead 

 of mere microscopic lines of growth. 



It is with some doubt that we have referred this little shell to the 

 genus Dentalium, because its small size and comparatively strong, regu- 

 lar costae, give it much the appearance of the non-spiral part of the 

 shell of a Ccecum. It is more arched, however, and more tapering than 

 we generally see in the body part of the shells of that genus, which are 

 likewise, we believe, unknown in any of the Paleozoic rocks. 



Position and locality Danville, Illinois. Hoof of No. 7 coal, of the 

 Illinois section of Coal Measures. 



DENTALIUM MEEKIANUM, Geinitx ? 



PI. 29, Fig. 8. 

 Dentdlium Meekianum, Geinitz, I8G6. Garb, und Dyas, ill Neb., p. 13, Tab. I, Fig. 20. 



Position and locality Same as the last. 



Genus ORTHO^EMA, M. and W., 1861.* 



(Proceed. Acad Nat. Sci., Phila., p. 146.) 



ORTHONEMA comcA, M. and W. 



PI. 29," Fig. 5. 

 Orthonema conica, MEEK and WOKTHEN, 1866. Proceed. Acad. Nat. Sci., Phila,, p. 270. 



SHELL elongate conical, thin. Volutions (in adult ex- 

 amples) about nine, flattened nearly on a line with the 



* For a description of this genus, accompanied by an illustration of the typical species, see Vol. II, 

 of the Illinois Geological Koports, p. 380, 1866. 



