ACTINOCRINID Z&. ae 
Calyx distinctly lobed at the arm regions, the higher orders of brachials 
forming, together with the ambulacral plates overlying them, five more or 
less prominent calicular extensions, or brachial lobes, from the two divisions 
of which the free arms are given off by alternate bifurcation from every 
second or third plate. The plates of the dorsal cup are ornamented by radi- 
ating ridges, which often meet in a node, Basals three, rather large, forming 
a well defined cup. Radials larger than any of the succeeding plates. Cos- 
tals two, the first hexangular — exceptionally quadrangular. Distichals all 
axillary ; supporting at their outer side an arm, at the inner from two to three 
palmars. The succeeding bifurcations take place in a similar manner; each 
successive order of brachials consists of two or three plates, of which each 
axillary supports an arm at one side, and two or three post-palmars — accord- 
ing to species — at the other, and so on to the last bifurcation in the calyx, 
which gives origin to two arms. When there are only four arms to the ray, 
the last bifurcation is on the distichals, and there is of course no alternation. 
The arms are given off alternately from opposite sides in almost the same 
way as the pinnules from an arm with a succession of syzygies; but in 
Actinocrinus the sides of the proximal arm plates are suturally united with 
the plates which support the succeeding order of brachials. Arms biserial, 
and frequently branching onee or twice after becoming free; the pinnules 
long, and their proximal joimts armed with a small hook, projecting from 
the middle of the plates. The interbrachial spaces on approaching the 
arm regions are widely and deeply depressed; they are occupied by numer- 
ous plates, which meet with the interambulacral pieces above, and in some 
species take part in the formation of the brachial extensions. The anal side 
is the widest, containing one large plate in line with the radials, which is 
followed by two interbrachials; the anus is located at the distal end of a 
strong tube, which rises abruptly from the summit of the tegmen. Orals 
rather small and excentric. The ambulacral plates either consist of two rows 
of large covering pieces, which pass out from between the orals and follow 
the branching of the food grooves, or are represented by large single plates 
of a first and second order, succeeded by small covering pieces, which meet 
with those of the free arms. Column round, the axial canal small and 
pentangular. 
Distribution. — Restricted to the lower part of the Subcarboniferous or 
Mountain limestone. In America it makes its appearance in the Waverly 
group, where it is represented, so far as known, by a single species; it reached 
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