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798 THE CRINOIDEA CAMERATA OF NORTH AMERICA. 
equal to, or greater than the length; their upper faces one third narrower; 
facets semicircular, directed upward, and occupying one half the width of the 
plates. Anal plate of a similar form to the radials, but narrower at the top, 
the upper portion somewhat bulging. Costals two, very short. Arms two 
from each ray, rather strong, biserial from the fifth plate ; flattened on the 
back. Arm joints twice as wide as long. Pinnules heavy and unusually 
long even for this genus. Column small; the nodal joints considerably 
widest, and their edges knife-like and serrated. 
Horizon and Locality. — Upper Burlington limestone ; Burlington, Iowa, | 
and several places in western Illinois and Missouri. 
Dichocrinus plicatus Hatt. 
Plate LX XVII. Figs. da, }. 
(1861. Hat; Boston Journ. Nat. Hist., Vol. VIL., p. 288. 
1881. W. and Sp. ; Revision Paleocr., Part IL., p. 84 (Proceed. Acad. Nat. Sci. Phila., p- 258). 
Of the type of D. striatus, which it resembles in the style of ornamenta- 
tion; but the plates are thicker, the ridges upon the plates comparatively 
larger, less in number, and the species is smaller throughout. Calyx globu- 
lar, slightly conical at the lower end; greatest diameter at the lower part of 
the radials, the upper part curving gradually inward. The ribs or ridges 
covering the surface are undulated and very strong, the intervening grooves 
deep and wider in the middle than at the ends. They form six well defined 
rhombs, distributed around the calyx in a similar manner as those in the 
preceding species; but their inner spaces are occupied by one or two in 
place of three to four ridges, and the triangles at each side of the rhombs, 
which are longitudinally divided by the interradial sutures, are smooth or 
only occupied by low pustules. | 
Basals longer than the radials, forming a deep cup with rounded sides 
and slightly truncated lower end. Radials subquadrangular, widest at the 
lower margin ; facets wide, occupying two thirds the width of the plate, and 
directed upward. Anal plate generally a little narrower than the radials. 
Costals two, small, supporting two arms. Arms thin, long; composed of 
rather long cuneate pieces, which interlock from the fourth or fifth plate. 
Pinnules stout and very long, the joints three times longer than wide, 
Column small. 
Horizon and Locality. — Upper Burlington limestone ; Burlington, Iowa. 
Types in the Museum of Comparative Zovlogy. 
