118 PAPERS, ETC. 
septum into two lobes of brain-shaped convolutions, the 
free portion of which extends over the visceral cavity. 
Obs. This species presents considerable variety, 
in most cases depending upon the completeness of the 
supra-membraneal disk. In the varieties presented by 
figures 4 and 5, the raised and solid portions’ only of 
the disk are preserved. This species has more punetua- 
tions than other oolitie forms, which are particularly 
numerous and large in the visceral cavity. 
From the inferior oolite of Dundry, and is not un- 
common. 
THECIDEUM DUPLICATUM.—Moore.—Plate 2, fig.”—12. 
Shell rather broader than long; valves convex; surface 
slightly granulated; attached by the upper part of the 
ventral valve; hinge line straight; deltideum small, de- 
pressed, triangular, under which is a small flattened space ; 
interior of the dorsal valve shews a regularly granulated 
margin, within which is araised granulated ridge, united 
in the centre by a septum, with an enlarged granulated 
base, from the top of which is thrown off on either side a 
high ridge, in the perfect shell covered in its whole course 
with irregularly shaped calcareous processes, which ap- 
pear in some instances long enough to reach the interior 
surface ofthe ventral valve; the ridge deseribing a circle 
returns towards the base of the central septum; over the 
visceral cavity is the bridge from whence two small pro- 
cesses depart. Interior of the ventral valve has a slightly 
raised septum, on either side of which are the impressions 
of the larger museles; above the septum is an elevation 
bounded by ridges, which received the insertion of the 
adductor muscles. 
