A remarkable receptacle, with the tentacula partially introverted, is figured Pict. Atlas, pl. xlvi. fig. 2, from Gloucestershire; and several beautiful examples of the arms, tentacula, &c. of Pentacrinites in Lias limestone and shale, in pl. li. figs. 9, 15, 16, and pl. lii. figs. 1, 2, 3, from Charmouth.
Rhodocrinus. (R. verus. Pict. Atlas, pl. xlix. fig. 7, 8.)—A beautiful form, allied to the Antinocrinoids, occurs in the palæozoic rocks, and is named the Rose-encrinite by Miller. The column is cylindrical and traversed by a pentagonal canal. The rays or arms arise by a single ossicle and then bifurcate: the receptacle is formed of three, five, ten, and more numerous series of plates, which are ornamented externally. A fine example of a crinoid of this type (Hypanthocrinus) from the Wenlock limestone, is figured in the London Palæontological Journal, pl. xxi.
In Sir R. Murchison's Sil. Syst. all the crinoids of the Silurian deposits, then known, are figured. Several new genera are described by Professor McCoy, in the Synopsis of British Palæozoic Fossils.
Eugeniacrinus (Clove-like Encrinite). [Lign. 92, fig. 1.]—These little crinoids, which resemble a clove in form, are found at Mount Randen, in Switzerland, in Oolitic limestone. The receptacle is simple in structure, for it has but one series of plates; its cavity is very small. It had five arms: the articulating surface of the ossicles is radiated. When perfect this crinoidean must have somewhat resembled the Lily Encrinite, but the plates are all anchylosed, or blended together, which Mr. Miller attributed to an early stage of growth.
PENTREMITES PYRIFORMIS.
Pentremites pyriformis (Pear-shaped angular Encrinite). [Lign. 91, fig. 2.]—The column of this remarkable crinoid is short, and formed of cylindrical, perforated ossicula, with radiated surfaces, and has irregular side-arms. The receptacle is composed of polygonal plates, divided by five perforated grooves or furrows, which are of an elongated petalous form, and converge in a rosette on the summit. The marginal longitudinal rows of minute pores are not however for the passage of soft membranous feelers, as in the ambulacra of echinoderms, as was formerly conjectured, but are channels for the transit of vessels that supply an infinite number of delicate simple tentacula, composed of extremely minute calcareous ossicula, as in the other Crinoidea, but not subdivided as in the Pentacrinites and Encrinites.
These articulated tentacula are arranged close together in longitudinal rows on the ambulacral spaces; there being two rows, each consisting of fifty tentacula, on every space. They are directed upwards towards the vertex of the receptacle, and appear to be the instruments for the capture and conveyance of food to the mouth.[287]
[287] See Dr. Fred. Röemer on jointed tentacles found on the ambulacral spaces of Pentremites, "Geol. Journal," vol. v. p. 8.
There are several species of Pentremites, some of which swarm in the cherty limestones of Kentucky. Mr. Say, to whom we are indebted for the first satisfactory investigation of these fossils, mentions that such is their abundance, that he has observed, on a piece of rock not larger than three inches by two-and-a-half, above twenty specimens lying in relief