550 GEOLOGY OF OHIO. 



where the flattened upper side of the shelf meets the regular and strong 

 curvature of the sides and the lower, ab-apical surface. There is no 

 umbilicus. The inner lip is slightly thickened and stands out from the 

 last volution. The striae are almost obsolete in some specimens. 



Pleurotomaria filitexta, sp. nov. 



(Plate 37 A., Figs 6 a, b.) 



This shell has quite a low spire, owing to the fact that the newer 

 whorls rise high up on the previous whorls, covering their slit- 

 band entirely. The upper part of each whorl (holding the initial 

 end of the shell upwards) is less convex than its sides, thus 

 assisting in the general depressed appearance of the spire. The shell 

 is 10 mm. wide, the spire shows an elevation of 1.7 mm. above 

 the surface of the end of the last whorl. It has 5 whorls. The total 

 height of the shell is hardly 6 mm. Along the middle of the side of 

 the volutions runs a slit-band which is barely two-fifths of one millimeter 

 wide near the mouth of the shell. It consists of a broad groove, bor- 

 dered on each side by a single striation, which is distinct, though but 

 slightly raised above the general surface of the shell. On the upper 

 surface numerous very regular, distinct, close, filiform, transverse striae 

 ornament the surface and curve back to the slit-band, forming with it 

 an angle of about 70 degrees, if no account of the more rapid backward 

 curvature at the slit-band itself be taken into account. Below the slit- 

 band, similar striae also curve backward to the slit-band. Near the 

 aperture about 22 strise were counted in a length of 2 mm. This species 

 was found in the " Orthoceras block" at Huffman's Quarry. 



Raphistoma affine, Foerste. 



(Plate 26, Fig. 18 ; Plate 37.1, Figs, 1 a, b, c.) 



Since the description of this species in the Bulletin of Denison 

 University Vol. I, the exterior of the shell has been observed in speci- 

 mens from Todd's Fork Ohio. The transverse striae are close and fine ; 

 from the junction of each whorl with the preceeding one, the striae bend 

 back strongly towards the quite sharp angle, which is formed at the 

 middle of each whorl, laterally. In a general way the striae form an 

 angle of forty-five degrees with the latter. In the* larger shells there is 

 commonly a very shallow depression on the upper surface of the last coil, 

 a short distance from its edge, which causes an apparent slight thickening 

 of the shell along the edge, especially towards the aperture. The mouth 

 is oblique, facing diagonally downwards ( if the apical end of the spire be 

 placed at the top). The largest specimen so far found had a greatest 

 diameter of 20 mm. The height of the spire varies considerably. It is 

 usually very low. The species occurs in the Beavertown marl at Huff- 



