Volltext Seite (XML)
Eciiinodermata.] LOWER PALEOZOIC RAHIATA. 57 hexagonal, and one pentagonal or heptagonal flattened plates, from which proceed two hands of three plates each (completing the cup) from whence the rays originate; one or two rows of large interbrachial plates between the secondary radial rows; a strong ridge runs up the middle of each of the primary radial rows, then dichotomising, one branch going to each of the secondary radial or arm rows; all the plates of the cup marked with thick radiating ridges, one usually passing through the middle of each side to the centre of the adjoining plates; one large octagonal or hexagonal 1st interradial (or intercostal plate,) supporting two or three 2nd ditto (or interscapular plates) ; column rounded or subpentagonal, the joints radiated or marked with five petalloid crenulated ridges. Like Periechocrinus this genus has the plates of the arms and hands, or secondary and tertiary radial rows, flattened, to form part of the cup instead of the rays; the chief distinctions between these genera being the distinctly quinquepartite pelvis and strongly radiated plates of Glyptocrinus. Glyptocrinus basalis (M r Coi/.) PI. 1. D. fig. 4. Ref.—M c Coy, Ann. Nat. Hist. 2nd Series, Vol. VI. p. 289. Sp. Cli.—Cup semipyriform; pelvic plates hexagonal, slightly exceeding the primary radials in length and supporting the interradials on their upper truncated edge; all the plates marked with thick radiating ridges, one to each side, except in the pelvic plates, which have them only to the three upper sides, the lateral pair being the forked ends of the strong vertical ridge of the primary radial rows; average length of cup from pelvis to base of free rays, one inch six lines; widtli the same; length of pelvic plates three and half lines; pentagonal 1st primary radial three lines; hexagonal 2nd ditto two and half lines; heptagonal 3rd ditto (scapular) plate three lines; hexagonal 1st secondary radial or arm-plate -two and half lines; 2nd ditto two lines. This fine species differs from the Glyptocrinus decadactylus (Hall.) of the Hudson River group of New York, by the great size of the pelvic plates, and their being hexagonal instead of pentagonal, and their bearing the interradial plate directly on their truncated upper edge, the interradial in the American species being supported on the sides of the laterally united 1st primary radials, which latter plates in this species are completely separated. The first of the secondary radial, or arm-plates, are laterally united without the intervention of an interbrachial plate, which exists, however, between the 2nd secondary radials, and nearly equalling them in size. In one of the most distinctly preserved interradial spaces, three 2nd interradials (interscapular plates) are seen to rest on the upper half of the octagonal 1st interradial, the lateral ones being pentagonal, and the middle longer one hexagonal. All the plates seem to have been thin and allow considerable variety in form of the cup from slight pressure. Position and Locality.—Not uncommon in the calcareous schists of Alt yr Anker, Meifod, Montgo meryshire. Explanation of Figures.—PI. 1. D. fig. 4. Natural size from the schists of Alt yr Anker, Meifod. Genus. EUCALYPTROCRINUS {Gold.) = Hypanthocrinus (Phil.) Gen. Char.—Column and alimentary canal round ; body very large, oval, mouth central, projecting; capital plates large, convex; rays very short, only reaching to the base of the mouth; pelvis small, concave; 1st primary radials five, hexagonal, each supporting a quadrangular 2nd primary radial, on which rests a pentagonal or slightly hexagonal 3rd primary radial (scapula), from the sides of which come off two rows of one or two secondary radials (arm-joints), often with one interbrachial plate between them ; each cuneiform secondary radial supports two free rays or hands, of two or more fingers, each finger of a double row of joints; five very large rounded polygonal 1st interradial plates, surrounded by the whole of the primary and secondary radials, supporting a pair of small ovate 2nd interradial plates, generally extending in a thick club-shaped ridge as far as the tips of the fingers.
