. The Devonian crinoids of the State of New York. Crinoidea, Fossil; Paleontology; Paleontology. DEVONIAN CRINOIDS OF NEW YORK 33 canal in Paleozoic crinoids. It may be no larger than the point of a needle or it may be one-half to three-quarters the width of the columnals. There is an extension into the axial canal of a vessel from each of the five lobes of the chambered organ with its nerve sheath (the axial cord). The five cords compris- ing the axial cord surround a prolongation of the axial organ. In dicyclic crinoids the cords would be radial; in monocyclic, interradial. Wachsmuth and Spr
. The Devonian crinoids of the State of New York. Crinoidea, Fossil; Paleontology; Paleontology. DEVONIAN CRINOIDS OF NEW YORK 33 canal in Paleozoic crinoids. It may be no larger than the point of a needle or it may be one-half to three-quarters the width of the columnals. There is an extension into the axial canal of a vessel from each of the five lobes of the chambered organ with its nerve sheath (the axial cord). The five cords compris- ing the axial cord surround a prolongation of the axial organ. In dicyclic crinoids the cords would be radial; in monocyclic, interradial. Wachsmuth and Springer (1897, p. 60) framed a " law " to the effect that when infrabasals are, or have been, present, the. DicLjcltc Monocyclic Figure 28 Diagrams of Dicyclic and Mono- cyclic bases showing the position of the cirri with reference to the plates of the dorsal cup. IB, infrabasal; B, basal; R, radial; ci, cirri; co, pentameres of column; n, nerves going to cirri from extensions of capsule; s, suture between pentameres of column. (After Bather 1898, 1900) exterior angles of the stem are interradial; but the longitudinal sutures, the sides, the lobes of the axial canal and the cirri of the stem are radial; in crinoids with a true monocyclic base the conditions are reversed. This is true only of species with a pentangular or pentapartite stem or canal. Bather points out (1898, p. 423; 1900, p. 106) that this law is liable to excep- tions; and he believes that a surer guide for discriminating between monocyclic and dicy- clic forms is obtained by attending chiefly to the rela- r tion of the axial cords. Figure 29 Relation of cirri to axial cords. A, part of stem The appendages of the of Isocrinus decorus, with cirri in whorls of five. 1 n A ' ' A +V, B, section across stem of Isocrinus wyville- COiumn are Called CIYYI and the thomsoni at level of cirrus-whorl, the central portions ossicles Composing them are disproportionally enlarged for greater clearness. C, section _ . ac
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Keywords: ., bookcentury1900, bookdecade1920, booksubjectpaleont, bookyear1923
