10 Cincinnatt Soctety of Natural Fiistory. 
upper face truncated the entire width of the plate, and separated 
from the second radial or brachial plate on the outer face by a 
strong suture, but immediately within a straight crenated ridge 
extends from one outer angle of the plates to the other, on the 
upper face of the plates, which is furrowed upon each side so as to 
form a toothed hinge upon which the second radial or first brachial 
articulates; behind this hinge, in the middle part of each plate, 
there is a depression or socket for the reception of a tooth-like pro- 
jection ; on the under side of the second radial or brachial, a dart- 
shaped furrow also extends on the upper side along the line of 
union of the plates, commencing just within the angle arising from 
the union of the crenulated ridges and extending to the interior of 
the cup which receives a corresponding projection from the second 
radials; second radials or brachials pentagonal, produced exter- 
nally in a more or less strongly developed spine, and bearing upon 
the upper or inner sloping sides the free arms, the first one or two 
plates of which are single, but above these composed of a double 
series of interlocking plates; when the arms are closed the pin- 
nules are within, and the body is compact something like an 
Encrinus; there are no regular interradials ; a single azygous inter- 
radial rests upon the truncated upper end of a subradial, between 
two first radials, and extends upward between the second radials or 
brachial plates; it is truncated at the upper end and followed by a 
single piece, beyond which the connection with the vault or pro- 
boscis is unknown. Type D. hemisphericus. 
The species upon which this genus is founded was first defined 
by Shumard under the name of Poteriocrinus hemisphericus, in 
1858, in the Transactions of the St. Louis Academy of Science, 
Vol. I, p. 221. Meek, in 1872, under the name of Scaphiocri- 
nus (?) hemisphericus, Shumard, in the Report on the Paleontology 
of Fastern Nebraska, p. 147, Pl. V., Fig. 1a, tb, and Pl. VIL, Fig. 
ta, b, c, redefined and illustrated Cyathocrinus inflexus of Geinitz, 
which is a distinct species as pointed out by Geinitz, though con- 
generic. In 1873, under the name of Scaphiocrinus (?) hemi- 
sphericus, Shumard, in Geo. Sur. Ill., Vol. 5, p. 561, Pl. XXIV., 
Fig. 5, Meek, probably, correctly identified and illustrated this 
species. 
In 1880, in the Proceedings U.S. National Museum, Vol. 2, p. 
257, White described a species under the name of Erisocrinus 
planus, which was redescribed and figured in Hayden’s Twelfth 

