A treatise on zoology . escribed, Rather, 1893), Silurian, Kurope,and probably N. America. Crown bent, in the transversal plane, backon the stem, which is then coiled around it in the opposite direction(Fig. LIX.). The coil could be tight, or could be uncoiled and the crownexposed ; the movement was ellectod by an clastic ligament towards theinner margin of the columnals, by strong muscles towardsthe outer margin, the fulcrum being a transverse ridge. Columnals show THE CRINOIDEA H7 traces of orip;inal pentaTnerism, hut over the f^roater part of the stem arecresceiitic iii sectio
A treatise on zoology . escribed, Rather, 1893), Silurian, Kurope,and probably N. America. Crown bent, in the transversal plane, backon the stem, which is then coiled around it in the opposite direction(Fig. LIX.). The coil could be tight, or could be uncoiled and the crownexposed ; the movement was ellectod by an clastic ligament towards theinner margin of the columnals, by strong muscles towardsthe outer margin, the fulcrum being a transverse ridge. Columnals show THE CRINOIDEA H7 traces of orip;inal pentaTnerism, hut over the f^roater part of the stem arecresceiitic iii section, the concavity heing on the inner niar^nn. Cirri,borne ou the horns of the crescent, vary in their arrangement in differentspecies. No root in adult. One r;iy missing ; otlier RR all compound,except 1. post. R somelimes ; x lower than in other lleterocrinidae, partlyrests on r. post. Hi (the radianal, RA). The tube outwardly resembles aseries of Rr and covering-plates. Arms slightly heterotomous. The ?;/ - •> -. c* > #r. w^ ^:?- .^^^^ -A^f^, te ^ Fig. LIX. Herpetocrinus Fletcheri, in its natural coiled position, the cirri wliicli covered the crownhaving been removed. C, cirri; S, longitudinal suture of stem ; t, anal tube. (After Bather,1893.) X f. remarkable resemblance of the coiled cirriferous stem to a pinnulate,canaliculate arm has misled most writers ; for the crown is rarely visible(vide-p. lS4:). Family 4. Calceocrinidae. Monocyclica Inadunata, withthe essential characters of typical Heterocrinidae, the 1. ant., r. ant, andr. post. RR being compound, and the arms branching primitively on theplan of Heterocrinus heterodactylus; but with the following modificationsinduced by the bending down of the crown :—the r. post. IR lies alongsidethe stem ; the 1. ant. R lies away from the stem ; the plane thus markedis one of a gradually increasing bilateral symmetry ; r. post, arm always 148 THE CRINOIDEA absent, its place being occupied by anal tube ; the tube encroac
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