408 SMITHSONIAN INSTITUTION 



Taxocrinus whitfieldi (Hall) 

 Plate LX, figs, i-ii 



Forbesiocrinus whitfieldi Hall, Geology Iowa, I, pt. 2, 1858, pp. 632, 633, fig. 104. — Hall, Supplement 

 Geology Iowa, i860, p. 88. — Meek and Worthen, Proc. Acad. Nat. Sci. Philadelphia, 1865, p. 140; 

 Geol. Surv. Illinois, II, 1866, p. 243. 



Onychocrinus whitfieldi, Meek and Worthen, Geol. Surv. Illinois, V, p. 552, pi. 20, fig. 3. 



Taxocrinus whitfieldi, Wachsmuth and Springer, Revision Palaeocrinoidea, I, 1879, P- 49- 



Forbesiocrinus cestriensis Hall, Supplement Geology Iowa, i860, p. 68. 



Forbesiocrinus parvus Wetherby, Jour. Cincinnati Soc. Nat. Hist., 1879, P- 138. pi- n. figs. 4a, b (Separate 



p. 5). 

 Taxocrinus wetherbyi Miller and Gurley, Bull. 6, Illinois St. Mus. Nat. Hist., 1895, p. 41, pi. 4, figs. 3-5. 



The last known survivor of Taxocrinus. 



A medium-sized species. Crown low and broad, much wider than high, 

 infolding about the lower IVBr, and expanding with a broad curve to that 

 level, where height to width is about 1 to 2 in mature specimens, somewhat 

 less in the young. Calyx a continuous wall to the level of upper IIBr except at 

 the anal side, with rays but little prominent and iBr areas little depressed; 

 height to width at IAx, i to 3.5; spread from base, 1 to 4. Side outline low 

 convex. Rays bifurcating about four times, the last one after infolding; 

 diminishing greatly at third division; free arms small and delicate; sutures 

 moderately sinuous. iBr areas wide, plates numerous and strong to level of 

 second axillary and followed by perisome. Surface smooth. Dimensions of 

 crown in maximum specimen: 17 mm. high; 35 wide; base, 6; in a small one, 

 7.5 mm. high; 10 wide; base, 2.2 mm. Average adult specimens about 12 mm. 

 high by 24 wide. 



IBB visible as low pentagons. BB large, sometimes connecting with iBr 



in one or more rays. RR and IBr of about the same width. IBr 3; IIBr 2, 



fully incorporated in calyx wall, two-thirds as wide as IBr; IIIBr 2 or 3 in 



inner ramus, 3 or 4 in outer ; higher divisions very narrow. iBr plates very 



large for three ranges of about equal size, a fourth one smaller followed by 



perisome; areas nearly flush with rays to height of IIBr 2, where they curve 



inward. Column large, with long conical enlargement of very thin plates next 



to calyx, below that cylindrical with alternating columnals. 



This species is the conclusion of the line of retrogression which marks the extinction 

 of the genus in the latest member of the Lower Carboniferous. It has several peculiar 

 features : The interbrachial structure in the regular areas is the strongest found in any 

 species of the Taxocrinidae, and this is correlated with an absolutely weak anal side, con- 

 taining nothing but perisome bordering the small tube ; of such strong bordering plates 

 as are seen in T. giddingei there is not a trace. It has the lowest and broadest crown of 

 any species; its habitus is that of a very broad, shallow basin (figs. 3a, 4) with arms fold- 

 ing over the rim as in figure 3c; wherever the specimens are preserved in a soft matrix 

 they retain the form shown in figures 1-4. I have 6 such specimens, and there is little 

 variation in their form and proportions; specimens like figures 5, 7, 9, 11 are laterally com- 

 pressed, and give an erroneous idea of the natural contour. 



