. The Devonian crinoids of the State of New York. Crinoidea, Fossil; Paleontology; Paleontology. 38 NEW YORK STATE MUSEUM rearrangement of the internal organs. The fixed larva is termed a penta- crinoid (figure 31). After fixation the orals become arranged in a pyramid over the superior or ventral portion of the animal, the basals form a similar, but inverted, pyramid in the proximal or dorsal portion of the calyx, the infrabasals occur between the apex of the basal pyramid and the top of the column. At this time the column is composed of about eleven cylindrical columnals and is terminated di
. The Devonian crinoids of the State of New York. Crinoidea, Fossil; Paleontology; Paleontology. 38 NEW YORK STATE MUSEUM rearrangement of the internal organs. The fixed larva is termed a penta- crinoid (figure 31). After fixation the orals become arranged in a pyramid over the superior or ventral portion of the animal, the basals form a similar, but inverted, pyramid in the proximal or dorsal portion of the calyx, the infrabasals occur between the apex of the basal pyramid and the top of the column. At this time the column is composed of about eleven cylindrical columnals and is terminated distally by a lobate terminal stem plate, the dorso- central. Each columnal consists of the original central ring and numerous longitudinal, parallel calcareous rods which have been developed from it. The larva is now in what is termed the cystid stage of development. For convenience, the development of the larva in the fixed state has been divided into two stages: (1) the cystid stage, stalked forms without arms; (2) the phytocrinoid stage, still stalked but provided with arms and cirri. Within a short time after fixation there appears in the diamond-shaped spaces between the divisions of the orals and the basals another series of five plates, the radials, which increase rapidly in size and encroach upon the orals. In one of the interradial spaces, in the zone of the radials, a sixth plate, the so-called anal, appears; larva of Antedon but it gradually moves up into the tegmen with the i^aoiis; b, biSS orals and is resorbed. This so-called anal has been centro-dorsai. (After silown bv A. H. Clark (1912), from a study of penta- Wvville Thomson, . ' !865). crinoid larvae, to be in reality the radianal ot the tossil forms. The true anal x has been found by him in the pentacrinoid larvae of other species of comatulids (see also, Springer's studies, 1920, pp. 79~&7, of larval forms of Comactinia meridionalis). From each radial is given off a series of elongate cylindrical segment
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Keywords: ., bookcentury1900, bookdecade1920, booksubjectpaleont, bookyear1923
