ON Tis IIKI3 SJ INCIS Ol WIVOQUSIEIS MUAIT IC IOS SUL 
MEDUSA IN 2th NIAGARA EIMESTONE 
OW INOURINSUTIUN INCIVIONOUS 4 
For more than a year past my attention has been directed to 
some peculiar fossils from the dolomitic Niagara limestone of 
northern Illinois, in the collections of Walker Museum at the 
University of Chicago and of the Chicago Academy of Science. 
The exact horizon and location from which the specimens were 
obtained have in no case been recorded, but the general local- 
ity for them all is Joliet, Ill. Additional specimens have recently 
been secured from the excavations of the Chicago drain- 
age canal, by Mr. L. H. Hyde, of Joliet, and these have been 
kindly loaned for study. 
The complete specimens of this peculiar fossil are disk-like 
impressions, subcircular in general outline, with the periphery 
lobed, and with the surface radiately corrugated or smooth. In 
the center of the disk is a funnel-shaped depression and from 
the center of this depression a stemlike process rises to about 
the general level of the surface of the disk. The disk is divided 
by four ridges, radiating at right angles from the center, into four 
quadrants. The entire disk is rarely preserved intact, the larger 
number of specimens being the separate triangular quadrants. 
Several species are represented in the collection which differ in 
t Just as this paper is going to press additiona] material from the collection of 
Mr. E. E. Teller, of Milwaukee, Wis., has come to the writer, which throws a very 
different light upon the nature of Cryptodiscus. One of the specimens in this collec- 
tion shows a complete disk of Cryftodiscus situated at the summit of a tube composed 
of plates which are arranged essentially as the plates in the anal tube of Callcrinus. 
The evidence of these specimens seems to establish the fact that Cryptodzscus is a 
remarkable disk-like expansion of the four plates forming the terminal ring of the 
anal tube of some crinoid, probably Cadcrinws. Additional evidence for the correla- 
tion of Cryptodiscus with Callicrinus is found in the fact that the genus Calhcrinus 
occurs at every locality where Cryptodiscus has been observed. The specimens in 
Mr. Teller’s collection will be illustrated and more fully described at another time. 
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