54 
SMITHSONIAN INSTITUTION 
INSERTAE SEDIS 
Nyctocrinus magnitubus new genus and species 
Plate 12, figs. 16-21 
Among- the Tennessee collections there is a form abundantly represented 
by well preserved specimens, of which after frequent reviews I have been 
unable to fix the systematic position. It is a dicyclic crinoid of Camerate aspect, 
with 5 IBB, suggesting the Dimerocrinidae ; but it has the RR in contact all 
around, with no anal in the cup, which excludes that family as well as the 
Rhodocrinidae. The dicyclic base excludes the Melocrinidae, and other Cam- 
erate families that might be suggested. Except for this, there would be a some- 
what near approach to the Platycrinidae. There are large RR, with one or two 
IBr, filling only part of the distal face, leaving well defined shoulders support- 
ing large iBr chiefly above the line of RR (perhaps more properly tegminal 
iAmb.), of which the posterior one seems to be rather the largest. Basals are 
large, curving into a shallow concavity, in which the 5 IBB form a broad, 
inverted cone. Arms are stout, biserial, 2 or 4 to the ray with occasionally 
another bifurcation. The most remarkable character is a long, spinose anal 
tube, which projects beyond the limits of the arms. 
Except for the well defined interbrachial plates resting on the radials, this form might 
fall under some of the dicyclic Inadunata ; but with our present knowledge it may as well be 
left in an intermediate position. In addition to the five specimens figured in which more or 
less of the arms and anal tube are shown, and the two giving perfect internal and external 
views of the base, there are half a dozen calices in which the same type of dicyclic base 
clearly appears — so that the definition of characters here given may be regarded as beyond 
question. It is a singular fact that all the speciinens in which the tube is shown differ from all 
others of the formation, even those in the same matrix, in being very dark in color — which 
suggests the generic name. 
Beech River formation, Brownsport group, Niagaran ; Decatur County, Tennessee. 
