54 SMITHSONIAN INSTITUTION 



PLATE XXIV 



PAGE 



Figs. 1-27. Forbesiocrinus nobilis De K. and Le H. (continued) 249 



(Also on Plates XXI, XXII and XXIII) 



A series of specimens showing the form and mode of articulation of the principal calyx and 

 arm plates. In general the arrangement of the figures is in the natural order, i. e. basal plates 

 below and brachials of successive ranges in ascending order. Being mostly detached and 

 weathered plates, and not all from the same individual, the size is not always proportionate to 

 their relative positions. Note the deep fossae in the apposed lateral faces of all the calyx 

 plates up to, but not including, lAx, and the change in mode of attachment from there up; 

 also the marked thickening of the plates upward. 



For convenience of reference, the proximal view is always drawn with the dorsal side up, 

 and the ventral view the reverse. Lettering in small type above the figures will help to identify 

 the respective plates and the view given : — thus IBri.d means primibrach i, distal view. 

 All figures are X 2, unless otherwise indicated. 

 Fig. 10. A regular basal, proximal view; showing articulation with infrabasals by broad, shallow 

 fossae, with deeper ones at the lateral faces. 

 lb. Another proximal view of same, showing lateral structure more plainly. 

 2a. A similar basal, dorsal view ; showing surface ornament, and sockets for patelloid processes 



of radials. 

 2b. Distal view of same plate, showing deep fossae at basi-radial sutures. 



3. Similar basal; direct view of upper sloping basi-radial suture. 



4. Posterior basal, distal view ; showing articulation with plates of anal interradius, 



So. First regular interbrachial, proximal view ; showing lower lateral faces of union with 

 radials. 



$b. Distal view of same ; faces of attachment by deep fossae to three interbrachials of second 

 range. 



6. Middle interbrachial plate of second range, distal face ; showing entire change in mode of 

 union with succeeding plates. Instead of fossae, as on the proximal face of this plate, 

 there are rugose ridges extending the full thickness of the plate, probably for attach- 

 ment of thick plated perisome ; a fossa is seen at the lateral face for union with 

 fellow interbrachials of the same range. 



7a. A radial, proximal view ; showing articulation with basals, and also the fossae at the 

 brachio-interbrachial sutures. Thickness of plate less than one-third of the width. 



/b. Distal view of same; fossa at lateral face meeting" first interbrachial. 



yc. Left lateral view of same ; showing fossae and marginal crenulations. 



8a, b, c. Primibrach i ; proximal, distal, and left lateral views. Note the three different modes 

 of union at the faces of this plate, viz. : by deep fossae at the sides (with iBr) ; by 

 bundles of ligament at the face meeting R ; by paired ligamentous articulation at the 

 face meeting the succeeding IBr. 



ga, b. Primibrach 2 ; dorsal and ventral views. The former shows the indentation and pro- 

 jection for the patelloid processes, and the latter the broad, smooth inner surface, 

 without any appearance of median grooves. On this plate the lateral connection by 

 fossae extends nearly to its full height. 



10a, b,c. Primibrach 2. Proximal, distal, and left lateral views of another specimen, in which 

 the change in mode of connection with interbrachials from deep fossae to rugose 

 ridges and furrows occurs about halfway up the plate. On the radial faces the 

 elements of a modified articulation by paired ligaments are sharply defined, viz. : 

 dorsal ligament fossae ; transverse ridge : interarticular ligament fossae : median 

 ridge with a groove along its middle. The median sinus is strongly marked with a 

 rather deep cavit}', which continues more or less defined throughout the ra.y — perhaps 

 a remnant of perforation by a dorsal canal. 



iia,b,c. Axillary Primibrach 3 = lAx. Proximal, ventral, and dorsal views; showing radial 

 articulation, the patelloid processes, and the sockets in which they engage. 



[2a. b. Axillary primibrach 3 = lAx. Distal and left lateral views of another specimen. The 

 lateral fossae are no longer seen, but the rounded rugose ridges with furrows which 

 seem to discharge, and sometimes to converge, toward the interior, are finely shown in 

 this and the next following figures, 14 and 16. These plates are nearly half as thick 

 as wide. 



