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614 THE CRINOIDEA CAMERATA OF NORTH AMERICA. 
pressed, the bottom concave to the middle of the first costals, which together 
with the first interbrachials and second anal plate are geniculated, or ab- 
ruptly bent upward, and swollen so as to form a circle of hemispherical 
nodes around the margin of the concavity; the upper portions being almost 
vertical. Ventral disk depressed pyramidal, with a short conical spine at the 
summit. Surface of plates throughout the calyx finely granulose, and suffi- 
ciently convex to bring out the suture lines. 
Basals hidden from view, occupying the bottom of the column concav- 
ity. Radials about as wide as long, all hexangular in outline. First 
costals slightly larger than the radials and quadrangular; the second not 
longer than the first, but often considerably wider, and provided with an 
obtuse mesial ridge, which connects with the prominences upon the first. 
The distichals from the second up are free. The arm facets have a slightly 
upward tendency, and those of the same ray are placed at right angles ; 
arms a little longer and more slender than in A. drevis. Interradial 
spaces wide and somewhat depressed in the upper portions, a little con- 
tracted at the arm regions. First interbrachial large, curving abruptly 
upward ; followed by two elongate pieces, and a small quadrangular one, 
the latter occupying the arm regions. The interambulacral plates consist of 
five or six pieces. The two lower anals vary considerably in size; the first 
being in some specimens not longer than the radials, in others almost twice 
as long. In the latter case the first takes part in the circle of nodes which 
form the lower margin of the calyx, in the other it occupies together with 
the radials the lower concavity, and the second anal is nodose and forms 
a part of the circle; the interbrachials at the sides of the second anal are 
elongate and widest in the middle. The next row consists of three smaller 
plates, which are succeeded by numerous irregular still smaller ones, forming 
an almost flat area. Anus directed laterally and placed low down, a little 
above the arm openings. Posterior oral large, high conical or subspinous ; 
the four others are scarcely elevated. The radial dome plates somewhat 
projecting and moderately convex. 
Horizon and Locality. — Upper Burlington limestone, Burlington, Iowa. 
Type in the Museum of Comparative Zodlogy. 
Remarks. — The circle of tumid plates at the lower margin of the calyx 
distinguishes this species from all others. 
