250 THE CRINOIDEA CAMERATA OF NORTH AMERICA. 
Interradial spaces wide, composed throughout of large plates, which connect 
with the disk plates, or, properly speaking, pass into the disk. The large 
plates between the radials are frequently surrounded by small supplementary 
or secondary pieces, which wholly or partly isolate them from the basals, 
radials and costals. The second range of interradials consists of two, excep- 
tionally three, pieces, the third of three; the latter forming part of the upper 
margins of the arm openings. The anal interradius, which is wider than the 
others, has three plates in the second, and four or more in the third row. 
Ventral disk depressed conical; composed of rather large plates, none of 
them conforming to the general arrangement of orals, which are probably 
unrepresented. Anus almost central, and at the end of a strong tube. 
Column round or indistinctly pentangular, with a large pentalobate canal. 
Distribution. — The three species herein described come from the Trenton 
group of Eastern Tennessee. In the same locality we found a fourth species, 
but none of the specimens so far obtained are sufficiently well preserved for 
description. 
Remarks. —We make our Diabolocrinus perplerus the type of the genus. 
Diabolocrinus has closer resemblance to Lyriocrinus and Archeocrinus than 
to Rhodocrinus, but is readily distinguished from both of them. In Lyrio- 
crinus the arm facets are directed strictly upwards, the arms are single 
and placed in a straight line with the walls of the dorsal cup; while in 
Diabolocrinus the arms were apparently given off as armlets from tubular 
prolongations of the calyx, and the facets are directed obliquely outward. 
Archeocrinus has a more elongate calyx, the disk consists of minute irregular 
pieces, it has no anal tube, and never supplementary pieces such as we find 
in D. perplecus. The latter is a feature that reminds us of Reteocrinus, Xeno- 
erinus, and Acrocrinus, in which a similar intercalation of plates takes place 
on a much larger scale. 
Diabolocrinus perplexus W. and Sp. (nov. spec.). 
Plate XI. Figs. 1a, b. 
Length of calyx as compared with its width three to two; pentangular 
across the arm bases; the dorsal cup more than twice the height of the 
tegmen ; basal concavity wide and moderately deep, involving nearly the 
whole of the basals. Plates convex, the larger ones bearing one or more 
conspicuous nodes, the others a single central one. 
