98 
SMITHSONIAN INSTITUTION 
and the inferradials of the lost arms, here meeting underneath the anal series to form a sub- 
anal piece. In figure 7 they are opened to about a right angle; while in figure 15 the very 
unusual condition is seen of the crown widely opened out almost to an erect position upon 
the stem. Some other figures, 8, 9, 10, are given showing in part the same structures, but 
more especially to illustrate the change in shape of the calyx due to growth, from elongate 
with nearly parallel sides in the younger individuals, to relatively short and widely spreading 
downward toward the base in the older. 
Mobility of the Crown 
With the establishment of the tri-radial symmetry in the group, the organism after an 
early beginning seems to have finally adapted itself to the recumbent habit as the position of 
rest, from which it could readily change as occasion required. The widely gaping articula- 
tions between radials and arms, and between many of the successive brachials, secured in 
addition to the larger movement upon the base the maximum of flexibility above the hinge 
line, whereby the arms could be flexed or extended by the contraction of their own muscles. 
Change of position of the crown was further facilitated by the curvature of the stem at its 
proximal end, as shown by the presence of wedge-formed columnals, by the articulation of 
which it could be bent or straightened to some extent. The closed condition is by far the most 
frequent as found in the fossils. Evidence of habitual pressure of the crown upon the stem 
is not uncommon in the form of deep indentations upon the anal plates, or in the Ordovician 
form upon the interray to the right of them, as shown in figures 17 of plate 28; 24 of plate 29, 
and 14, i 6 a of plate 30. In others equally firmly closed, the indentations are not present, the 
pressure being relieved by the slight proximal bending of the stem. 
Excellent illustrations of the adaptability of the crown to these movements are afforded 
by figures 5 of plate 28 and 17, 18, 19 of plate 30, with the crown lying closely recumbent 
upon the stem, and figure 21 of plate 28 in which it stands almost at a rig'ht angle, and figure 15 
of plate 30 before mentioned in which it is extended almost in the same line. 
The expression “ bending of the crown upon the stem ” recalls the structure of the pre- 
ceding Heterocrinid derivative, Myclodactyhis, to which the same term might be applied. 
There, also, is some diminution of radials due to pressure or a cramped position, accompanied 
by a specialization of stem in its way equally remarkable with this. But the change in direc- 
tion of the crown is accomplished by simple curvature of the stem; there is nothing in the 
structure analogous to the hinge and the consecpient mobility of the crown upon the base. 
M ode of Life 
The question arises, what is the relation between the extreme departure of the crinoids 
of this family from the usual habitus of crinoids and their mode of life? Primarily, all such 
modifications have to do with the food supply and the mode of obtaining it. In some genera, as 
Torynocrimis, the arms are bent from the calyx to one side, from which presumably the food- 
bearing currents came. In others, such as Monohrachiocrinus and Abrachiocrinus, the arms 
have progressively been reduced in number and finally eliminated entirely, because, as is sup- 
posed, the crinoids lived in an environment where the food was brought to them by the cur- 
rents in such quantities that arms were no longer needed to gather it. 
Elere, in the form now before us, not only the arms w’^ere affected by the adaptation to 
unusual conditions, but the entire crown above the base was forced out of its natural upright 
position on the stem. It has hitherto been generally assumed that the crown had become 
habitually pendent upon the stem, so that while the stem itself remained upright, the normal 
position of the crown was reversed, and the arms pointed downward, with, however, some 
power in the crinoid, by means of the hinge between basals and radials and the muscular 
articulation, to raise itself to a horizontal or partially erect position. This supposition was 
