﻿220 



NEW YORK STATE MUSEUM 



The value of study under the dammar mounting may now be seen 

 by an examination of plate 5, figures 2 and 4. In the former the 

 area of figure 1 is again presented, but the fragmentary matter 

 covering the epithecal canals has been rendered more transparent by 

 the mounting medium and the band of carbon deposited by the 

 decaying b.vs. brought more clearly to view. The boundary between 



this darkened belt and the 

 clearer calcite of its side 

 walls is well marked and 

 makes the measurement of 

 the canal diameters an easy 

 matter. Their full width is 

 found here to be from .10 

 to .12 mm. This agrees 

 closely with that of the as- 

 cending ridges of text fig- 

 ure 7 and the uncovered 

 regions on text figure 8. 



Plate 5, figure 4, presents 

 portions of the two radials 

 over r.post.B. The longer 

 canal of the horizontal 

 series shows not only its 

 cylindrical character but 

 its floor as well. Near the 

 suture this floor dips into a 

 depression whose deeper 

 portion is filled with limon- 

 ite-colored mud. This 

 darker area seems also to 

 graph, xio b e w id er an d to run under 



the remote edge of the canal where the latter reaches the suture. 

 We have here an oval basin whose major axis crosses the sutures 

 and whose minor axis is nearly twice as wide as the bore of the 

 exothecal canal which enters it on the left. 



The basin just described is but the outward expansion of a sutural 

 canal and below it two others as well shown. The sutural canal next 

 above the one with the longest exothecal canal was weathered out 

 more completely and for some time after mounting its communica- 

 tion with the interior was made manifest by the bubbles of air which 

 rose from it and moved away through the thin mounting medium. 



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Fig 8 View of a portion of the holotype of Palaeo- 

 crinus striatus Billings. From a photomicro- 



