506 THE CRINOIDEA CAMERATA OF NORTH AMERICA. 
others pass out to the costals and first interbrachials, and from one to three 
to the other plates; but only those of the middle series are continuous, the 
two at the sides which form the inner triangles, when present at all, being 
interrupted and less distinct. 
Basals large, forming a broad cup, with rapidly expanding sides; the 
lower margins projecting over the top of the column, somewhat thickened, 
and slightly notched at the sutures; the axial canal sharply pentangular. 
Radials large, longer than wide, the sloping upper faces much smaller than 
the lateral ones. First costals nearly as long as wide, scarcely half the size 
of the radials, and hexangular; the second costals from one third to one 
half smaller than the first. Distichals small, twice as wide as long, axil- 
lary; their sloping outer faces support an arm, which becomes free from the 
second plate, the inner faces two palmars (rarely one or three), of which the 
upper 1s axillary and gives off a single arm at one side, at the other post- 
palmars and two arms. Arms forty, of moderate size, simple through- 
out, slightly tapering, and somewhat flattened toward the extremities; the 
plates transversely angular. Pinnules long, their two or three proximal 
joints covered with small hooks. First interbrachials a little larger than the 
first costals, supporting two plates, followed by four, of which the two lower 
are in part interambulacral, and the upper ones touch the orals. Occasion- 
ally there are two additional plates between those of the second and third 
rows. Anal interradius very wide; the anal plate succeeded by two plates 
in the first, three in the second, and five in the third row; those of the 
latter, which occupy the equatorial zone, are followed by irregular pieces in 
the tegmen. Tegmen very short; the plates moderately large, slightly 
convex, their surfaces rugose. Orals comparatively small, especially the 
posterior one, which is smaller than the others, and is placed at the sidé of 
the anal tube. Tube nearly central, long, heavy throughout, and frequently 
curving; the plates sharply nodose and transversely arranged. The ambu- 
Jacral plates, covering the calycine extensions, decrease in size outward, 
and are immovable; those of the first and second orders consist of large 
single pieces, but those of the higher orders of two rows of plates. Col- 
umn proportionally small, composed in the upper part of thicker and 
thinner joints, the former widest at the top; but at 50mm. from the calyx 
all joints have nearly the same dimensions. 
Horizon and Locality.— Upper Burlington limestone, Burlington, Iowa, 
Quincy, Ills., Hannibal, Mo., and other places. 
