MEDIN AN, NIAGARAN, AND • CHESTER FOSSILS 95 
is less convex than its sides, thus assisting in the general depressed 
appearance of the spire. Along mid-height of the last volution 
is a narrow slit-band, bordered on each side by a single striation, 
which is distinct, though but slightly raised above the general 
surface of the shell. General vertical outline of the volutions 
rounded, without revolving ridges, striae, or grooves, excepting 
only the groove of the slit-band. All surface striae transverse. 
Umbilicus open, as far as known. 
Genotype. — Pleurotomaria fiUtexta Foerste. 
Cryptaulus filitextus (Foerste) 
Pleurotomaria filitexta Foerste, Geol. Surv. Ohio, Pal. VII, 
1893, p. 550, pi. 37A, figs. 6a, b. 
Shell 10 mm. wide, and scarcely 6 mm. high. Volutions 5, 
the spire rising 1.7 mm. above the surface of the last volution. 
Slit-band barely 0.4 mm. in width near the aperture. Here 22 
transverse striae occur in a width of 2 mm. These striae curve 
backward along the upper surface of the last volution so as to 
form an angle of about 70 degrees with the slit-band until within 
the immediate vicinity of the latter, where the transverse striae 
curve more strongly backward. Along the lower side of the 
slit-band the transverse striae also curve backward on approach- 
ing this band. 
Locality and formation.^ — Found at the abandoned Huffman 
quarry f mile southeast of the Asylum for the Insane, in the 
southeastern part of Dayton, Ohio, in the Brassfield limestone. 
Remarks.' — The general appearance of Cryptaulus filitextus 
is that of a Helix, but provided with a slit-band at mid-height 
of the last volution, the slit-band of earlier volutions being covered 
up successively by the later volutions. No other Silurian shell 
with exactly the same type of structure is known. 
Pleurotomaria aequilatera (Wahlenberg), as figured by Lind- 
strom^^ is similar in its general Helix-like form, its open umbilicus, 
and the presence of a slit-band at mid-height, or only slightly 
above mid-height of the volutions. Figure 27 on the plate cited 
Lindstrom, Silurian Gastropoda of Gotland, 1881, pi. 9. 
