. The Devonian crinoids of the State of New York. Crinoidea, Fossil; Paleontology; Paleontology. DEVONIAN CRINOIDS OF NEW YORK 25 crinus (plate 3, figures 1, 6) where the pore is situated at the end of a tubular interradial appendage (ref. cit., pp. 45, 46). b Arms The arms of a crinoid are the immediate prolongations of the radials. The simplest type of a crinoid arm (figure 22) is made up of a series of ossicles, the brachials, the proximal one of which is attached to the radial by a surface known as the radial facet or arm facet. The dorsal side of the arm is rounded and the inner or ventra
. The Devonian crinoids of the State of New York. Crinoidea, Fossil; Paleontology; Paleontology. DEVONIAN CRINOIDS OF NEW YORK 25 crinus (plate 3, figures 1, 6) where the pore is situated at the end of a tubular interradial appendage (ref. cit., pp. 45, 46). b Arms The arms of a crinoid are the immediate prolongations of the radials. The simplest type of a crinoid arm (figure 22) is made up of a series of ossicles, the brachials, the proximal one of which is attached to the radial by a surface known as the radial facet or arm facet. The dorsal side of the arm is rounded and the inner or ventral side is provided with a groove which contains the soft parts. Beneath this ventral groove the brachials. Figure 23 Specialization of arm-branching. 1, a nonpinnulate, regularly dichotomous arm (isotomous); 2, a less regularly dichotomous arm, a type common in the Cyathocrinoidea; 3, 4, two stages in the evolution of unilateral heterotomy; 5, 6, 7, three stages in the evolution of bilateral heterotomy. (After Bather, 1900). are perforated by the single (sometimes duplicate) axial canal which con- tains the double-structured dorsal nerve cord. The ventral groove is roofed over by covering plates, the ambulacrals. In less simple arms these covering-plates may be separated from the brachials by the adambulacrals or side plates. As described under Tegmen, the ventral grooves with the soft parts contained within them and the covering plates are continued across the tegmen to the mouth. The covering-plates are movable on the arms and pinnules, but on the disk only in those forms in which the mouth is exposed. As discussed under the description of the dorsal cup, the brachials may be free immediately above the radials or a variable number of the. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Goldring, Winifred,
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Keywords: ., bookcentury1900, bookdecade1920, booksubjectpaleont, bookyear1923
