CRINOIDEA.
Char.—Body with ramified rays, supported temporarily or permanently on a jointed calcareous stem ; alimentary canal, with mouth and vent, both, as in Bryozoa, approximated.
The " stone-lilies," or crinoid star-fishes, formed a nume rous and important group in the palwozoic seas, where they obtained their maximum number and variety. M. d'Orbigny describes thirty-one paheozoic genera, two triassic, ten oolitic, and four cretaceous—of which latter three (Pentaerinus, Bow guetierinus and Comatuia) are found in the tertiaries and mo dem seas. The Crinoidea differ from the other echinoderms in having the generative organs combined with the arms, and opening into special orifices near their base. Nearly all the t. Spheeronites aurantium, Wahl. , L. Silurian, Sweden.
2. Pseudocrinus bifasciatus, Pearce ; U. Silurian, Dudley.
3. Pentremites florealis, Say ; Carboniferous, Ohio.
4. Crotalocrinus rugosus, Mill. ; U. Silurian, Dudley.
5. Poteriocrinus (joint of column) ; Carboniferous, Yorkshire.
6. Encrinus entrocha ; L. Muschelkalk, Germany.
7. Apiocrinus Parkinsoni, Mill. ; Bradford Clay.
8. Pentacrinus basaltiformis, Mill. ; Lias, Lyme.
9. Marsupites ornatus, Mill. ; Chalk, Sussex.
genera, except Comatula and Marsupite.s (fig. 6, 9), appear to have been attached either by the expanded base of the column, as in Apiocrinus, or by jointed processes, as in Bourgueticrinus. In many instances the lower part of the column throws out innumerable root-like side-arms, which strengthen and support it. The column is comparatively short in Apiocrinus Parkin soni, and extremely elongated in Pentacrinus Bierneri. It is round in nearly all the palpozoic Crinoids ; and when five sided, the articular surfaces of the joints are simply radiated, as in the rest. These joints are perforated in the centre, and when detached, are the " St. Cuthbert's beads" of story (fig. 6, In Platycrinus the stem is compressed, and the arti cular surfaces are elliptical. In the genus Pentacrinus, which commences in the liar, the sculpturing of the articulations is more complex (fig. 6, 8), but it is quite simple in the other modern genera. The body of the Crinoid is composed of poly gonal plates forming a cup, which is covered by a canopy of smaller plates. The mouth is often proboscidiform ; the anal
orifice is near it. The five arms which crown the cup are sometimes nearly simple, but feathered with slender, jointed fingers ; in other genera they divide again and again, dichoto mously ; and in two remarkable Silurian forms, Anthocrinus and Crotalocrinus (fig. 6, 4), these subdivisions are extremely numerous, and the successive ossicles are articulated to each other laterally, forming web-like expansions, similar in appear ance to the coral Fenestrella (fig. 3, 11). Other remarkable Silurian Crinoids belong to the genera Glyptocrinus, Eucalyp tocrinu.s, Geocrinus (the " Dudley Encrinite") and Caryocrinus. Several are common to the Silurian and Devonian, as Me locrinus, Cyathocrinus, and Rhodocrinus ; the two last, and Poteriocrinus, extend into the carboniferous formations. Cu pressocrinus and some others are peculiarly Devonian ; Platy minus, common to Devonian and coal formations ; and many genera (including the " nave Encrinite"—Actinocrinus, Gil bertsocrinus, and TV oodocrinus), are proper to the carboniferous limestone. The famous " lily Encrinite" (En4winus entrocha, fig. 6, 6) is characteristic of the middle trios, or " muschel kalk ;" the " clove Encrinite" (Eugeniacrinus, fig. 7, 9) abounds in the Oxfordian oolites of Germany ; Apiocrinus, Milleri crinus, and several forms related to Comatula—e. g., Pterocoma and Saccosoma —are also peculiarly oolitic. The " tortoise • Casts, in chert, of the canal which passes down the crinoidal column are called " screw stones ;" and those limestones which abound in columns and detached joints are called " entrochal marbles." Encrinite" (Marsupites, fig. 6, 9), is found only in the chalk, along with Bourgueticrinus (fig. 7, 10) ; and the bodies of Co niatuice, which, when they have lost their arms and claspers, are called " Glenotremites." (Fig. 7, 7,—upper surface with sockets of the five arms ; s,—under surface, showing articula tions of claspers, and the scar of the larval stem.)