Contributions to Invej^tebrate Palaeontologij . 605 



forming varices at regularly increasing distances. Right valve also marked 

 by similar fine strije, but with the varices very indistinctly marked, or barely 

 perceptible under a lens. 



The species is a very strongly marked one, and very characteristic 

 of the Coal Measures. Mr. Meek describes indications of faint radii 

 between the varices on the examples from Illinois, but which do not 

 appear on specimens from Ohio so far as observed. The right valve 

 figured occurs close by the other, and is evidently of the same indi- 

 vidual ; the features are very similar, differing only in the absence 

 of the strong concentric varices. 



Formation and Locality. — In a thin layer of chert of the Coal 

 Measures, near the farm of Mrs. Banks, Falls Township, Hocking 

 County, Ohio. 



GASTEROPODA. 



Genus NATICOPSIS McCoy. 



Naticopsis Ortoiii. 



Plate XVI, figs. 12 and 13. 



Naticopsis Ortoni Whitf., Ann. N. Y. Acad. Sci., 1882, p. 230. 



Shell small, with a somewhat depressed conical spire, which forms an angle 

 of about 105 degrees, and the two and a half to three volutions are obliquely 

 flattened on their upper side, in the direction of the spire ; the outer one 

 being marked just below the siiture by a barely perceptible concave channel 

 of considerable width, which produces a very slight angularity of the upper 

 part of the volution. Suture-line slightly grooved. Lower side of the volu- 

 tion rounded ; umbilicus closed ; callus slight ; aperture obliquely ovate at 

 the outer margin, but rounded within from the excessive thickening of tlie 

 shell. Surface of the shell marked by fine, rather equal and somewhat regu- 

 lar transverse striae of growth, most distinctly marked on the lower half of 

 the volution. On the outer half of the last volution, there occur lines of nodes, 

 very faintly indicated, having a direction opposite to the growth-lines, and 

 becoming fainter and finally imperceptible toward the lower side. 



The species resembles N. nana M. and W. (Geol. Rept. 111., vol. 

 iii, p. 365, pi. 32, fig. 4) in size and general form, but differs from 

 it in the greater flattening of the volution in the direction of the 

 spire and in the faintly nodose surface. 



Formation and Locality. — In a thin cherty band of the Coal 

 Measures in the railroad cutting at Mrs. Banks's farm, Falls Town- 

 ship, Hocking County, Ohio. 



