594 NEW SPECIES OF CRINOIDEA, 
angles are inserted in the retreating angles formed by the union of the hexagonal plates of the first series ; 
two are irregularly heptagonal, and one hexagonal: these repose on the upper edges of the heptagonal 
plate of the first series. Hach of the above-mentioned quadrangular plates is surmounted by a widened 
pentagonal plate, which again supports on its oblique upper edges two short irregular pieces, sub-hexagonal 
or pentagonal, with their superior margins slightly concave to accommodate the arm-bearing plates, which 
are small and somewhat horseshoe-shaped. All the pieces which we have mentioned above the basal 
plate are elevated in their centres, which gives to the surface of the visceral cup an uneven appearance. 
The coronal integument is made up of numerous polygonal plates. The central one is a little larger 
than the rest, and is garnished with a spinous process, which is often produced to half an inch in length ; 
the others are usually tumid in their centres and wrinkled ; in some specimens, however, they are furnished 
with projecting tubercles, some of which are flattened and divided into two or more points. 
Mouth sub-central, protrusive but not proboscidiform. It is situated near the inner extremity of a 
prominent ridge composed of small, irregularly-shaped plates. This ridge commences at the central spinous 
plate, and terminates at the outer border of the cup between two of the arms. 
Arms twelve, bifurcations unknown. Column undiscovered. 
It occurs rather abundantly in the subcarboniferous limestone at Burlington and Augusta, Iowa. 
MEGISTOCRINUS. (N. G.) 
Generic character.—Basal plate tripartite, hexagonal, divisions equal. rst series of plates six, five 
hexagonal, and one pentagonal; second series thirteen, hexagonal; third series nineteen, five pentagonal, 
eight hexagonal, six heptagonal. These are surmounted by six ranges of polygonal plates, each range 
becoming successively smaller, and the plates more numerous in the ascending order. Coronal integu- 
ment composed of numerous polygonal plates. Proboscis a little below the superior rim, short and 
slender. 
MEGISTOCRINUS EVANSII. (N. 8.) 
(Tab. V. A, fig. 3, a, 6.) 
Synonym.—Actinocrinus Evansii, vol. ii., part i., p. 68, Jour. Acad. Nat. Sci. 
Specific character.—The body of this fine species has the form of an inverted truncated cone, with a 
moderately rounded base. Basal plate large, somewhat massive, flattened, slightly concave near the 
margin, moderately convex towards the centre. Impression for the attachment of the column large, 
occupying nearly one-half the diameter of the plate, slightly excavated and striated on the margin, per- 
foration large, obscurely pentagonal. First series of plates large, moderately convex, bent inwards and 
slightly upwards near their inferior margins, projecting below the plane of the basal plate, and not 
visible on the side view of the fossil. All the plates forming the sides of the cup are smooth, and 
slightly convex on the surface. Coronal slightly elevated, pieces of various dimensions, the larger ones 
mammillated in the centre. 
Proboscis short and slender; column and arms unknown. 
Dimensions.—Height, twenty-five lines; width at summit, thirty-two lines; width at base, thirteen 
lines ; diameter of basal plate, seven lines.’ 
Formation and locality.—It occurs with the preceding species in the lower series of carboniferous 
limestone at Burlington, lowa. For the magnificent specimen figured we are indebted to John Evans of 
the United States Geological Corps, and to him we have dedicated it. 
PLATYCRINUS. Miller. 
PLATYCRINUS AMERICANUS. (N. 8.) 
(Tab. V. 3B, fig. 1, a, 5.) 
Calyx.—Subglobose, surface ornamented with numerous prominent granule. Basal plate pentagonal, 
flattened ; surface for the attachment of the column small, round, finely striated in radii, with a minute 
Seeeah pacfocxtion. From the edge of this surface five petnclbi rows of granulz radiate to each angle 
of the’ plate, the intervening spaces being likewise granulated. Superior plates five, rather broad, in- 
creasing slightly i in width from below upwards; articular facet for the arms small and shallow. The 
granule are usually disposed over the surface of these plates, as follows: a row commences at each of 
