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 perpkxus the type of the genus. 

 Diabolocrinus has closer resemblance to Lyriocrinus Sind Archceocrinus than 

 to Hhodocrinus, 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. 

 Archceocrinus 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. perplexus. The latter is a feature that reminds us of Reteocrinus, Xeno- 

 crinus, and Aerocrinus, in which a similar intercalation of plates takes place 

 on a much larger scale. 



Diabolocrinus perplexus W. and Sp. (nov. spec). 

 Plate XL Figs, la, 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. 



