78 SMITHSONIAN INSTITUTION 



PLATE XXXVI 



(All figures natural size except where otherwise stated) 



PACK 



Figs. 1-7. Ichthyocrinus corbis Winchell and Marcy 285 



Fig. I. A typical specimen in the condition as usually found in magnesian limestone, with all 

 plates removed by chemical action, leaving a cast (made by the substituted matrix) 

 of the inner surface of the test, with sharp ridges or fine lines at the sutures. The 

 lower part of the calyx is unsymmetric, being thrown out of line of vertical axis by 

 excessive convexity at one side, and corresponding concavity opposite. Basal view, 

 showing small RA as inferradial under r. post, ray, smaller than RR in other rays; 

 small BB, probably not larger than column facet, and cast of space for IBB which 

 were probably resorbed. The convexity in this specimen is at the anterior side. 



2. Basal view of similar specimen, with the convexity at the posterior side, showing that the 

 distortion is not due to anal structures ; RA very small. 



3a. Left posterior radial view of a maximum specimen, perfectly rotund except for the usual 

 distortion at the base, where the convexity is at the right anterior side, Shows the 

 general contour of crown; the 4 IIBr; and the space for the resorbed IBB repre- 

 sented by a plug of the infiltrating matrix. 



3&. Direct view of base of same, showing outline of BB, and plug filling space for the 

 resorbed IBB. X 3- 



4. Smaller specimen, right posterior radial view ; convexity at left anterior side. Note small 



size of RA. 



5. Still smaller specimen, basal and right posterior interradial view; convexity at left anterior 



side. 



6a. A very large specimen, with part of the plates remaining; viewed from convex side of 

 calyx, orientation not ascertainable owing to injury of base. Shows that the sutures 

 are externally sinuous, although straight at the inner surface as always appearing in 

 the casts; 5 IIBr in some rays of this specimen. 



6b. View of same with convexity to the left, showing the original plates above the primi- ■ 

 brachs, with obscure radial ridges. 



6c. Outline vertical section ; to show relative thickness of plates, especially their extreme 

 thinness in lower part of calyx wall, indicating the probable manner of distortion 

 from weight of viscera. Composed from specimens 3 and 6; shaded lines in base 

 represent space of resorbed IBB. 



7. Young specimen figured by S. A. Miller (Jour. Cinn. Soc. Nat. Hist., Vol. IV, pi. 4, fig. 5) 

 as the true / corbis, having the plates preserved. Figured here for comparison ; its 

 elongate calyx, straight sides, and large BB, showing clearly that it belongs to 

 /. suhanguJarls, and not to this species. Chicago Academy of Science. 



Niagaran, Racine dolomite ; Silurian. From quarries at what was formerly 

 Bridgeport, now in the City of Chicago, Illinois. 



Figs. 8-12. Ichthyocrinus conoideus Ringueberg 283 



Fig. 8a. The type figured by Ringueberg, 1. post, radial view; appears more rapidly expanding than 

 the average of numerous specimens, partly due to flattening. 

 8&. Basal view of same, showing small, but well developed IBB; RA under r. post. ray. 



9. Cotype used in description, sHghtly flattened ; showing the extreme narrowness and 



slight spreading of calyx as usually found ; the absence of radial ridges ; and the BB 

 visible only as points. 



10. Large flattened specimen, showing crown to IIIBr4, and small size of BB in side view. 



11. Outline of a rotund specimen, showing about the normal contour of crown. 



12a, 6. Lateral and basal views of specimen with very high brachials, and yet the usual low BB. 

 Niagaran, Gasport limestone ; Silurian. Lockport, New York. 



