FOSSIE MEDUSAS IN THE NIAGARA LIMESTONE 747 
creature is abandoned for two reasons: First, the specimens 
are not mere impressions in the rock, but are cavities with an 
upper and a lower side, from which the actual solid substance of 
some fossil has been dissolved. In the second place there is no 
reason why the mere impression in the mud of the umbrella of 
medusez, should generally break into regular quadrants and be 
preserved as such. If we consider, however, that the specimens 
of Cryptodiscus are the casts of the gastric cavities of meduse. 
both of these difficulties are eliminated. The gastric cavities of 
some living meduse are divided by thin partitions into four 
pouches.’ If such a gastric cavity were filled with a fine sediment, 
and if after the decomposition of the soft parts of the creature, 
this cast should become fossilized, it is easy to imagine that the 
four lobes of the cast might often become partially or wholly sepa- 
rated or destroyed during the process. The one serious objec- 
tion to this theory is that probably the material originally filling 
the cavity of the medusa would be so nearly identical with that 
in which the cast was buried, that it would not be leached out, 
as would the shell of a brachiopod, for instance, which was of a 
different character from the matrix in which it was buried. 
DESCRIPTION OF SPECIES. 
In reading these descriptions and examining the illustrations, 
it should be kept in mind that they have all been drawn from 
the impressions in the limestone and are consequently the 
reverse of what the actual fossil would be. That is, what is 
described as a groove in these impressions would be a ridge in 
the actual fossil. 
Cryptodiscus corrugatus n. sp. Figs. 1-2. 
Disk 7 to 10™ in diameter, finely and deeply lobed on 
the periphery. Funnel-shaped depression in the center 10 to 
15™™ in diameter on the plane of the disk, narrowing below to 
the base of the central stemlike process which is from 3 to 5™™ 
across and rises 6 to 8™™ to the general plane of the disk. Sur- 
™See figure of a Calycozoon (Lucernaria), CLAUS and SEDGWICK, Text-Book of 
Zoology, Vol. I, p. 257, Fig. 197. 
