270 ILLINOIS ACADEMY OF SCIENCE 
mented with elevated revolving lines which are alternating in 
size, a weaker line occurring between two adjacent stronger 
ones. About ten of these lines occur in a space of 2mm. The 
revolving lines do not become weaker near the suture, nor do 
they become obsolescent in the umbilicus; the raised lines are 
separated by depressed interspaces about equal in width to the 
lines. Numerous fine transverse lines and occasional coarser 
lines of growth cross the revolving ridges and furrows in a 
direction obliquely backward from the suture, and give to the 
surface a finely cancellated appearance. 
Shells of this species are common in the Orchard Creek shale 
both north and south of Thebes. They occur also, though 
less abundantly, in the overlying Girardeau limestone in the 
same region. 
CONULARIDA 
Conularia delicatula, n. sp. 
Plate I, Fig. 10 
Description: Shell moderately large, pyramidal in form, 
quadrangular in transverse section, the sides gradually diverg- 
ing from the apex to the aperture. The sides of the shell seem 
to have been somewhat convex and the angles apparently fur- 
rowed. The surface on each side is marked by a series of fine, 
close, transverse lines of which there are about 20 in a distance 
of 1 mm. These are directed slightly upward toward the 
aperture as they approach the angles. 
Besides the numerous fine transverse raised lines and fur- 
rows, and occasional stronger transverse ridges or wrinkles, the 
fine transverse furrows are set at close intervals by minute 
tubercles or interruptions in the depressions, which under a lens 
are in places seen to be arranged in vertical rows in such a way 
as to resemble very fine longitudinal striae, and give to the 
entire surface an extremely delicately ornamented appearance. 
This species occurs sparingly in the lower part of the Thebes 
sandstone in the vicinity of Thebes, Illinois. It is readily dis- 
tinguished from other late Ordovician species of this genus by 
the very delicate character of its surface ornamentation. 
