. Elementary text-book of zoology, tr. and ed. by Adam Sedgwick, with the assistance of F. G. Heathcote. OIUXOIDEA, 289. tacrinus form (P. Europceus) (fig. 233), consists of a complicated metamorphosis. The greater number of Crinoids belong to the oldest periods of the history of the earth (the Cambrian, Silurian, Devonian, and the Carboniferous formations). Existing forms live mostly at considerable depths. We distinguish two orders, the Tesselata and the Articulata. The latter is represented by numerous fossil forms, but by only a few living genera as Penta- crinus, Holopus, and Comatula (fi
. Elementary text-book of zoology, tr. and ed. by Adam Sedgwick, with the assistance of F. G. Heathcote. OIUXOIDEA, 289. tacrinus form (P. Europceus) (fig. 233), consists of a complicated metamorphosis. The greater number of Crinoids belong to the oldest periods of the history of the earth (the Cambrian, Silurian, Devonian, and the Carboniferous formations). Existing forms live mostly at considerable depths. We distinguish two orders, the Tesselata and the Articulata. The latter is represented by numerous fossil forms, but by only a few living genera as Penta- crinus, Holopus, and Comatula (fig. 234). The cup is always less completely provided with plates than in the fossil Tesselata. ARTICULATA. Fain. Pentacrinidse. Crinoids with ten arms, several times bifurcated. There is a pentagonal stalk with whorled cirri. Pentacrinus caput Mi'dvsa?, Mill, from the Antilles. P. Miilli'ri Oerst, West Indian Ocean. The fossil forms are : Encrimis liUifvnnis Schl. (fig. 234) from the Muschelkalk ; also Ajjiocrimts, allied to the existing Rlttzoeriints lofotensis Sars, and to Batliycrinus fjracilt'x, and ahlricltianvs W. Th., from the deep sea. Allied to this group is the third existing genus Jlolojms, from the West Indies, with calj'x attached by a short pIG_ 234.— Encrinutlilii- unjointed prolongation of its apex. //. Raiigli d'Orb. fm-mis from the Mus- Fam. Comatulidse. Stalked only in the young state. chelkalk. The adult animal is free. There are usually ten arms at the margin of the flattened body ; mouth and anus are present. The Coma- iul idee possess the power of striking their arms towards the ventral surface and so of propelling themselves amidst the sea-weeds. The vermiform larva, with its four ciliated girdles, makes its appearance within the egg-membranes. It acquires a mouth and anus, also a tuft of cilia at the posterior end of the body, and swims about freely. It passes later, by the formation of cal- careous rings and rows of plates, into the stage of the stalk
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