060 THE CRINOIDEA CAMERATA OF NORTH AMERICA. 
sides expanding regularly from the base to the top of the costals, the higher 
brachials horizontal. Ventral disk depressed convex, occupying about one 
third the height of the calyx. Surfaces of plates somewhat variable, but, 
as a rule, the radials and anal plate strongly nodose, the nodes transversely 
arranged, covering the whole surface of the plates, and extending obliquely : 
outward. From the sides of these nodes indistinct ridges or angularities 
pass out to the costals, giving to the section of the cup an obscurely pen- | 
tangular outline; similar ridges proceed to the basals. The first inter- 
brachials are marked with very prominent rounded tubercles, rising 
abruptly at the middle of the plates, while the higher interbrachials are 
nearly flat. 
Base short, deeply grooved at the sutures, and notched at the lower 
margins, presenting three well marked lobes, which, hanging downward, 
enclose the proximal stem joints. Radials nearly as large as both costals 
<acaiabaia . = 
together, and as wide as long. First costals hexangular; the second wider 
than long, and generally smaller than the first. Succeeding brachials small, 
exteriorly rounded, with deep longitudinal grooves at the sides. Distichals 
Ste SSS 
all axillary, their sloping outer faces giving off an arm, the inner ones of both 
ray divisions two palmars, and these again an arm from the one side, and 
two post-palmars from the other, of which the axillary supports two arms. 
Arms forty (not twenty as supposed by Hall, nor thirty as given by Meek | | 
and Worthen); long, rounded, not branching in their free state, and not ; 
tapering at the extremities. Interbrachial spaces slightly flattened; they | 
consist at the regular sides of 1, 2, and 4 plates, the latter row on a level | 
with the arm openings, and at the anal side of 2, 3, and 5 pieces. Plates 
of the tegmen of medium size; the orals, which are slightly the largest and 
not in contact with each other, placed at some distance from the summit. 
Ambulacral plates of first and second orders represented by large single 
plates, those of the higher orders by rows of small covering pieces. Anal 
tube central, and of moderate size. | 
Horizon and Locality.— Upper Burlington limestone, Burlington, Iowa, 
and at the same horizon in Missouri and Illinois. 
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Types in the (Worthen) Illinois State collection, Springfield. 
