594 THE CRINOIDEA CAMERATA OF NORTH AMERICA. 
from one third the height of the calyx in large specimens to scarcely one 
fourth in smaller ones. Plates of the cup convex and of rather uniform size ; 
their surface ornamentation exceedingly variable. In most specimens, the 
middle part is bare of all markings, but along the margins of the plates there 
are at each side from one to three elongate processes or short ridges, and 
between them along the suture lines deep pits, which almost penetrate the 
test. In other specimens there are continuous ridges covering the whole 
surface, which give to the plates a reticulate or cancellate appearance ; while 
in still others rows of bead-like elevations take the place of the ridges. 
Basals forming a low, cylindrical cup, which is somewhat grooved at the 
sutures. Radials and costals of nearly the same size, and all as long as wide; the 
first costal a little smaller and hexangular, the second heptangular. Distichals 
1 X 10, about half the size of the axillary costals, and all axillary; the higher 
orders of brachials much smaller, and rounded like arm plates; the bifurcation 
being alternately from every successive plate. There are generally two or 
more orders above the palmars, sometimes three, and in young specimens occa- 
sionally but one; the number of arms, therefore, varies from four to six in 
the main branches, and from eight to twelve in the ray. Arms given off alter- 
natelyfrom opposite sides, and the proximal one free above the second plate, 
the others above the first; they are below medium size, long, and rounded 
on the back. Pinnules covered with small hooks. Regular interbrachials from 
eight to ten, in six or seven ranges. Anal plate as large as the radials; 
followed by 2, 8, 3, 3, 4 and two plates. Interdistichals two or three. Inter- 
brachials as well as the interdistichals in contact with the plates of the disk. 
Ventral disk deeply plicated around the margin; the plates small, generally 
smooth, and of nearly the same size and form. Column of nearly uniform 
size to about 6cm. from the distal end, where it gives off strong branches 
at irregular intervals, and tapers gradually to a sharp point. The nodal 
joints are a little the longest and widest near the calyx, but become indeter- 
minable farther down; axial canal of moderate size. | 
Horizon and Locality. — Upper and Lower Burlington limestone ; Burling- 
ton, Iowa, and at several localities in Missouri. 
Type in the (Worthen) Illinois State collection, Springfield. 
Remarks. — This species has been divided up into several varieties, based 
upon certain variations in the ornamentation of the plates, which cannot be 
recognized in large collections; and McChesney described a young specimen 
as a new species. As arule, in the smaller specimens the tegmen is more 
