TAXOCRINIDAE 405 



Taxocrinus giddingei (Hall) 

 Plate LIX, figs. 1-12 



Forbesiocrinus giddingei Hall, Geology Iowa, I, pt. 2, 1858, p. 633, pi. 17, figs. 2, 4. — Meek and Worthen, 



Proc. Acad. Nat. Sci. Philadelphia, 1865, p. 140. 

 Taxocrinus giddingei, Wachsmuth and Springer, Revision Palaeocrinoidea, pt. I, 1879, p. 48. — Keyes, 



Geol. Surv. Missouri, 1894, p. 223. 

 Forbesiocrinus elegantulus Miller, Bull. 4, Geol. Surv. Missouri, 1891, p. 40, pi. 5, figs. 14, 15. 



A very small species. Crown short and wide, broadly spreading below, 

 widest about the axillary primibrach, where height to width is about 1.1 to 1. 

 Calyx low, with broadly curving sides ; spread from base, i to t>-2. Rays wide, 

 convex, fairly prominent, tapering suddenly beyond the secundibrachs to rela- 

 tively slender branches, and infolding shortly beyond third bifurcation. 

 Sutures slightly sinuous, interbrachial areas wide, with numerous strong 

 plates followed by perisome. Surface smooth. Dimensions of crown, average 

 of specimens including the smallest and largest: height, iy mm.; width, 15 

 mm. ; base, 4.2 mm. 



IBB low, resembling a thin columnal. BB small, acute-angled. RR the 

 largest plates in the calyx. IBr 3, two and one-half times as wide as long, 

 slightly tapering to the axillary which is a little wider; IIBr 3, almost as large 

 as IBr; IIIBr 4, exceptionally 3 on the inner ramus, only half as large as IIBr 

 and followed by slender arms; higher brachials wider than long. Anal area 

 considerably wider than others; tube small, resting in socket at right upper 

 corner of post. B, bordered by strong plates on either side, sometimes as large 

 as the tube plates, and making post. B look as if angular above. Column 

 large, with proximal enlargement composed of uniformly thin columnals fol- 

 lowed by long and short ones alternating. 



This is a remarkably constant species in size ; in 30 specimens the variation lies between 

 15 mm. and 20 mm. in height, with scarcely any extremes beyond these. The secundibrachs 

 are constant at 3 for all the specimens. The anal side is in a transition " stage towards 

 Forbesiocrinus, having in some specimens a considerable resemblance to that of F. multi- 

 brachiatus. The Taxocrinoid character of the species is well fixed, however, by the condi- 

 tion of the interbrachial areas with their well-defined crescentic distal margin (PL LIX, 

 figs. 5, 8, etc.) followed by perisome (fig. 10). S. A. Miller's Forbesiocrinus elegantulus 

 (PL LIX, fig. 11) is founded on an average specimen from the typical locality, where the 

 species is fairly abundant in the upper beds. I have referred to it a form occurring sparsely 

 in the Keokuk beds at Canton, Indiana, which ranges a little larger in size, and might prove 

 different if we had better material for comparison. 



Types. Hall's original is in the American Museum of Natural History, New York ; 

 Miller's in the University of Chicago ; and the other specimens figured and studied are in the 

 author's collection. 



Horizon and locality. Lower Carboniferous, Warsaw Group and top of Keokuk ; from 

 the upper beds at Boonville, Missouri, and perhaps rarely in the somewhat lower Keokuk 

 beds at Canton, Washington County, Indiana. 



