590 NEW SPECIES OF CRINOIDEA, 
more recent number been removed to the genus under consideration, to which in the number of its supe- 
rior plates, and the form of the basal plate, it more properly belongs. 
In the United States, we are acquainted with five species appertaining to the genus Dichocrinus, all of 
which are from the carboniferous strata of the Mississippi Valley, and differ from any known European 
forms. 
The opinion advanced by Messrs. Austen, that all the Crinoids occurring in the carboniferous limestone, 
with six superior plates, will be found to have a bi-partite basal plate, is fully borne out by our investiga- 
tions. We have inspected a large number of specimens from the carboniferous rocks of various localities 
in Kentucky, Indiana, Illinois, and Iowa, and have invariably found this association to prevail where the 
superior plates rest immediately on the basal plate. 
DICHOCRINUS OVATUS. (N. 8.) 
(Tab. V. a, fig. 9, a, 8.) 
The body of this beautiful species, when deprived of its arms, is of an ovoidal form. 
Basal plate bi-partite, cup-shaped, hexagonal, thin, rounded; upper margin undulated to receive the 
orbicular edges of the superior plates; circle of attachment a the column slightly excavated, small, 
circular, and surrounded by a row of small and short spines. The surface of the plate is ornamented by 
depressed granulz, arranged in rows, some of which commence at the margin of the excavation for the 
supra-columnar joint, and proceed to each angle of the plate ; other lines run parallel with the undulating 
edges of the plate, forming a series of hexagons, one within the other, giving to the whole surface an 
exceedingly neat and elegant appearance. 
Superior plates six, of which five are elongated, quadrilateral, rounded at the inferior edges, and sup- 
port the arms; one is trapezoidal, wide, slightly angulated below and narrow above. The articular sur- 
faces for the arms, situated on the superior edges of the five arm-bearing plates, are moderately large, 
very slightly excavated, striated on the margin, with a transverse ridge near the centre. All the supe- 
rior plates are finely corrugated on the external surface. 
Arms.—Several joints of the arms remain attached to one of the superior plates, in the only specimen 
we have been able to procure of this species. The first joint is of a rectangular form, and supports a 
cuneiform joint, on the bevelled edges of which is the commencement of two series of smaller plates. 
Each of these joints is distinctly corrugated on the dorsal surface. 
Dimensions.—Height, nine lines; greatest width, 8 lines; diameter at summit, six lines. Height of 
pelvis, three lines ; height of superior plates, five lines. 
The column is undiscovered. 
This is one of the most beautiful species with which we are acquainted. It was obtained from the 
quarries in the carboniferous limestone at Burlington, where it is exceedingly rare. 
DICHOCRINUS STRIATUS. (N. 8.) 
(Tab. V. a, fig. 10, a, d.) 
Body globose, and composed of thin plates. 
Basal plate hexagonal, bi-partite, hemispherical, superior margin undulating ; circle of attachment for 
the column small, slightly excavated, finely striated in radii, with a minute round perforation in the 
centre. The surface is marked with permanent thread-like striz, some of soe begin at the excavation, 
ee originate near the middle of the plate, and radiate to the superior margi 
iperior plates six, five of which bear the arms; these are quadrilateral, ‘ckail ids elongated, wider 
saddy than at the summit, with the articulating surface for the arms, as in the preceding species, 
situated on their superior edges. The non-ray-bearing plate is trapezoidal, wide, slightly angular at the 
base and narrow above. The strix on this series of plates range in lines parallel to the lateral borders, 
and join those in the basal plate. Some of the strie are bifurcated near the upper margin, and when 
examined with a lens, have an undulated appearance. The furrows between the striw are crossed at 
irregular intervals by transverse threads. 
Formation and localities.—Occurs at Burlington in the cuiteiten layers of the carboniferous limestone, 
immediately above the oolitie members. It is not an abundant species. 
