. The Devonian crinoids of the State of New York. Crinoidea, Fossil; Paleontology; Paleontology. DEVONIAN CRINOIDS OF NEW YORK 17 because it will prove necessary to a clear understanding of the discussion of the arms. The tegmen may be in the form of a coriaceous skin with a large number of imbedded thin calcareous ossicles or it may be a plated disk (figure 9; plate 19, figure 4; plate 20, figure 8; plate 33, figure 2). The mouth (peristome) is more or less central and leads into an oesophagus or gut which is at first directed downward to the bottom of the cup by a dextral curve; then it rise
. The Devonian crinoids of the State of New York. Crinoidea, Fossil; Paleontology; Paleontology. DEVONIAN CRINOIDS OF NEW YORK 17 because it will prove necessary to a clear understanding of the discussion of the arms. The tegmen may be in the form of a coriaceous skin with a large number of imbedded thin calcareous ossicles or it may be a plated disk (figure 9; plate 19, figure 4; plate 20, figure 8; plate 33, figure 2). The mouth (peristome) is more or less central and leads into an oesophagus or gut which is at first directed downward to the bottom of the cup by a dextral curve; then it rises along the side of the cup and discharges through a usually excentric inter- radial aperture, the anal opening or anus. Inmost Figure 9 isocrinus all of the recent crinoids the arms and the pinnules a s *e r *a' Teemen ^ snowing very thin per- borne by them are each provided on the ventral sur- isomic plates, central r •.-, ci mouth, 0, and excen- lace with an open groove or iurrow known as the tric anuSj As_ (After ambulacral furrow. These ambulacral furrows unite Springer, 1913). at the base of the arms, forming five larger furrows which traverse the teg- men to the mouth. Below the floor of the ambulacral furrow in each arm is an epithelial nerve band and under this occur, in the order mentioned, the canals of the blood and water vascular systems, paired subtentacular nerves (one each side of the water vessel), paired subtentacular canals, the canal containing the geni- 1 2- 3 4 tal rachis and the dorsal coeliac canal. A large Figure 10 stages m the sepa- nerve cord of the dorsal system, the axial cord, ration of an axial canal, exemplified by brachials of lies below all the other canals and is deeply buried G i s s o c r i n u s g o n i o - within the caicare0us substance of the plates. By dactylus. i, youngest; ^ J 4, oldest, x 6 diam. (After the outgrowth of stereom the groove in which this dorsal nerve or axial cord lies is often separated from the brachial groove dur
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Keywords: ., bookcentury1900, bookdecade1920, booksubjectpaleont, bookyear1923
