FOSSIL MEDUSA IN THE NIAGARA LIMESTONE 745 
the lobing of the periphery and in the ornamentation of the disk. 
As in the case of most of the fossils in this formation, the actual 
substance has been dissolved out leaving a mold in the rock, 
and the specimens which have been collected are generally but 
one side of a thin disklike cavity. None of the specimens have 
been actually observed zm sztu, but it is believed that the speci- 
mens usually collected, viz., those with the central depression 
and elevation, are the lower sides of such cavities. The upper 
sides are not so striking in appearance, and have usually not 
been preserved by collectors. A few have been observed, how- 
ever, and they differ from the lower sides in being nearly plane 
over the central part, the funnel-shaped central depression with 
the central stemlike process being absent. Figure A represents 
diagramatically a cross-section of the fossil, cutting the disk 
diametrically. 
Fic. A. £f points upon the periphery of the disk. / the funnel-shaped depres- 
sion in the center of the lower side. s the stemlike elevation in the center of the 
funnel-shaped depression. 
In examining the literature, two references have been found 
to fossils similar to those under consideration. The first of 
these is in the Twentieth Report of the Regents of the New 
York State Cabinet of Natural History, where Dr. James Hall, 
on Plate XJ, Fig. 18, gives an illustration of a similar fossil, also 
from the Niagara limestone. No description of the specimen is 
published further than the note in the explanations of the plate, 
which is as follows: ‘‘The calyx of a Crinoidean? of a new and 
peculiar type, for which I suggest the name Cryptodiscus.” No 
locality for the specimen is given, but the species in the accom- 
panying paper are all from southeastern Wisconsin or northern 
Illinois. 
Ata more recent date, in the Eighteenth Report on the Geol- 
