128 SMITHSONIAN INSTITUTION 



PLATE LXI 



(All figures natural size except where otherwise stated) 



PACE 



Figs. 1-16. Parichthyocrinus nobilis (Wachsnnith and Springer) 412 



Fig. la. The type, distorted and imperfect as to base and anal side, being all that was known when 

 the species was described ; antero-lateral view. Shows rays from first bifurcation up, 

 and the maximum number of iBr known in this species at the exterior. 



i&. The same from radial view to the right. iBr plates in one interradius numbered for 

 comparison with next figure ; only three visible at the exterior. 



ic. Inner surface of plates of the interradius marked in fig. lb; showing the 3 iBr which 

 appeared on the outside, here much larger in area, and 4 more which did not come 

 through. 



id. Proximal face of plates shown in ic, showing wedge form of iBr; the plate alongside of 

 No. I narrowing to a point before reaching exterior of calyx wall. 



2a, b, c, d. Dorsal, ventral, right and left lateral views of a fragment of I. post, ray of same 

 specimen, containing R, three IBr, and one IIBr, being the plates next to the anal 

 area ; numbered for comparison ; i ^ R. They show the totally diflferent form of 

 these plates at the exterior and interior, and their singular modification by proximity 

 of anal structures, from which some of the brachials are crowded entirely away; 

 e. g. in this set No. 3 does not reach the inner surface, while No. I, the radial, is 

 enormously enlarged, and extended inward next to the anal area. The right margin 

 (2c) is perfectly rounded, showing the complete absence of any sutural attachment 

 to anal plates. , 



Sa,b,c,d. Dorsal, ventral, distal and lateral views of another detached fragment from same 

 specimen, having parts of 2 rays, and accompanying iBr. The 8 iBr that are visible at 

 the exterior (sa) are numbered; 6 more besides these are well developed at the 

 interior (3&) ; 3c and 3d show how those that do not come through are wedged in 

 between the brachials, sometimes two deep, tapering to fine points or edges, while the 

 brachials taper oppositely to fit them. This specimen explains the essential nature of 

 interbrachials as supplementary plates, developed at the inner, side of the test to fill 

 up spaces between the rays and their divisions, as the growth of the visceral mass 

 caused expansion of the calyx. 



4. Distal face of axillarj' IIBr, from same specimen. X 2. 



5, 6. Proximal and distal faces of IIIBrs. X 2. 

 7,8. Proximal and distal faces of IVBrs. X 2. 

 9. Proximal face of VBr. X 2. 



These specimens show the gradual development of an ambulacral furrow, from 

 none at all in the lower brachials, to a distinct groove with space for side pieces, 

 toward the distal region. 



100. A remarkably perfect, mature specimen, somewhat flattened ; anterior view, showing the 

 close interlocking of the rays above the iBr areas. 



10&. Posterior view of same; showing the small anal tube, not suturally connected with adja- 

 cent rays, and how the posterior rays close above it. 



11. Basal view of another specimen, anal side to the left. Shows form of post. B, with anal 



series rising from a socket probably below its distal margin; and the rounded margins 

 of posterior rays, not adapted to sutural attachment — a perfect Taxocrinoid- anal 

 side. Note the small size of r. post, radial. 



12. Posterior view of a similar specimen, somewhat crowded, so that 1. post. R partly overlaps 



post. B, concealing the shoulder to left of tube plates. 



13. Anterior view of a mature specimen, showing maximum development of iBr. 



14. Less mature specimen, with part of stem, posterior view ; showing post. B (partly covered 



by I. post. R), the anal structures, and the much reduced r. post. R. Note the peculiar 

 narrowing of one or more IBr toward the anal area, sometimes to a knife-edge, not 

 reaching margin of the ray at all, — a feature common to this genus, resulting from the 

 curvature of the posterior rays over the anal area. 



1.5. Young specimen with only one interbrachial. 



16. Still younger specimen, in which interbrachials have not been developed. 



Upper Burlington limestone; Lower Carboniferous. Burlington, Iowa. 

 All specimens are in the author's collection. 



