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Show 1004 MR. F. A. BATHER ON UINTACRINUS. [Dec. 17. 6. EXPLANATION OF THE PLATES. PLATE LIV. Structure of Uintacrinus socialis. Fig. 1. The apical system of specimen e, iu E 6327. X 3. Fig. 2. Articular or joint surface of a normal brachial, showing oblique fulcral ridge. X 10. Fig. 3. Ditto. X 24. Fig. 4. Joint-surface of a syzygial brachial. X 9. Fig. 5. Ditto. X 10. Fig. 6. Joint-surface of a normal brachial from the proximal region of the arm. X 6. Fig. 7. Joint-surface of a normal brachial. X 4. Fig. 8. Joint-surface of a normal brachial from the proximal region of the arm; the two halves of tbe fulcral ridge appear to be at an angle to one another, x 13. Fig. 9. Joint-surface of a normal brachial, showing at top right-hand corner tbe facet for tbe pinnule. X 4. Fig. 10. Joint-surface of a normal brachial; the fulcral ridge runs in a direction at right-angles to that in figs. 2 & 3. X 4. Fig. 11. Portion of an arm, showing origin of pinnules, the fourth joint from tbe right is a syzygy. X 4. Fig. 12. Joint-surface of a pinnular, showing axial canal with ligament-depression on either side. X 30. Fig. 13. A single brachial, bearing on its right side a pinnule, of which ten ossicles are preserved. X 6. Fig. 14. Portion of a pinnule from the ventral side ; tbe pinnulars are slightly shifted, so that portions of their proximal joint-surfaces are seen. X 12. Figs. 1, 11, 12, 13, 14 are by F. O. Pickard Cambridge, the rest by the author, and are all taken from E 6327. PLATE LV. An attempt at an exact restoration of Uintacrinus socialis, represented as swimming, five alternate arms raised, and five in the act of depression. Tbe various twists and coils of tbe arms are but slightly modified from actual specimens. The length of tbe arms is based on calculations from the specimens (see pages 987-8). The drawing was made of the natural size, by M r. F. O. Pickard Cambridge, under the direction of the author, and has been reduced photographically to about one-sixth natural size. PLATE LVI. Uintacrinus socialis. This is a reproduction of Clark's (7) plate i. from Bull. U.S. Geol. Surv. no. 97. The electrotype of the original block was very kindly sent by Mr. C. D. Walcott, Director of the U.S. Geological Survey, and m y best thanks are due to him for permission to use it. Fig. la. "Lateral view of the test, with interradial area central, natural size." This clearly is taken from one of the specimens figured by Meek (3). Compare text-figure 2, page 976. Fig. lb. "Test with arms." This also is doubtless natural size. Fig. Ic. " A radial [*. e. interdistichal] area, magnified two diameters." |