CRETACEOUS. ‘ 101 
Genus DISCOPHYLLUM Hall. 
DISCOPHYLLUM PELTATUM Hall. 
Pl. XLVII, figs. 1 and 2. 
Discophyllum peltatum Hall, 1847, Pal. N Y., Vol. I, p. 277, Pl. LX XV, fig. 3. 
Body consisting of a somewhat circular, flattened expansion, composed mainly 
of radiating fibers, which enlarge as they recede from the center, and terminate in a 
thickened border. 
This fossil appears to have consisted originally of a semihard circular or oval 
body, with firmer rays, reaching nearly or quite to the margin. The body becomes 
thicker and apparently harder toward the margin, and the rays are nearly concealed 
in its substance. This disk may have been attached by a smaller stipe, proceeding 
from the lower side, some obscure evidence of such an appendage existing. 
Two specimens of this peculiar fossil have been found, one in 1822 and the 
other a few years since, showing that it is an exceedingly rare form. It is quite 
unlike any other fossil known in our older strata. 
Position and locality.—This species occurs in the partially metamorphic arena- 
ceous shales of the Hudson River group, near the nail factory, below Troy, where the 
only known specimens have been found. (Cabinet of Troy Lyceum; cabinet of 
Professor Cook.) 
Observations — Through the courtesy of Prof. J. M. Clarke, I have had an 
opportunity of studying the type specimens described by Professor Hall. 
There is little to add to his description, except to note the presence of fine, 
concentric, undulating lines that cross both the rays and the interspaces 
between. ‘There is also indicated on the larger or broken specimen, fig. 2 
of Pl. XLVII, a ring surrounding an area about 2™ in diameter. The 
rays, however, cross the ring to the center. This may be the result of the 
compression of the specimen, so as to bring the opposite side down to a 
point opposite an aperture of which the ring is the margin, or the ring may 
be simply a stage in the growth of the specimen. 
It is exceedingly difficult to determine whether D. peltatum is the 
impression of a medusa. There is no a priori reason why a gelatinous disk 
should not leave such an impression in the very fine arenaceous silt which 
now forms the slightly gritty layers embedded in the shales carrying the 
eraptolitic fauna referred to the Trenton terrane. If D. peltatum be con- 
sidered to be the cast of the impression of a medusa, it might be grouped 
with Medusina princeps as an acraspedote medusa. In order to present to 
the student all the information available, a plate illustrating the two type 
specimens is introduced (Pl. XLVIT). 
