39 2 SMITHSONIAN INSTITUTION 



Taxocrinus juvenis (Hall) 

 Plate LIV, figs. 3-11 



Forbcsiocrinus juvenis Hall, Boston Jour. Nat. Hist., VII, 1861, p. 319; Prelim. Descr. new species 

 Crinoidea, 1861, p. 8; Bull. I, New York St. Mus., Photographic Plates, 1872, pi. 7, fig. 3. 



Taxocrinus juvenis, Meek and Worthen, Proc. Acad. Nat. Sci. Philadelphia, 1865, p. 140; Geol. Surv. 

 Illinois, II, 1866, p. 271. — Wachsmuth and Springer, Revision Palaeocrinoidea, I, 1879, p. 49. — 

 Whitfield, Mem. Amer. Mus. Nat. Hist., I, 1893, p. 35, pi. 3, figs. 21, 22. 



A variable species, usually of small size. Crown elongate, turbinate below, 

 with narrow base; height to width at second axillary, 1.5 to 1. Calyx to I Ax 

 almost as high as wide, about i to i.i ; spread from base, i to 2.8, with side out- 

 line gently curving. Arms tapering rapidly from IIBr to fine extremities, in- 

 folding usually about the third bifurcation; sutures broadly sinuous to arcuate. 

 iBr spaces wide, plates small passing into a strong perisome. Surface smooth. 

 Dimensions of type: crown, 18 mm. high by 11 mm. wide; base, 3 mm.; an un- 

 usually large specimen is 33 mm. high by 18 mm. wide, but the average of seven 

 specimens as usually found is about 13 mm. high by 9 mm. wide. 



IBB low, visible; BB fairly large. RR and IBr about twice as wide as long, 

 of similar form and size throughout. IBr 3 ; IIBr usually 4, sometimes 3 in part 

 of the rays, of nearly uniform size. Higher brachials in rather long divisions 

 diminishing rapidly at each bifurcation. iBr small in average specimens, with 

 strong perisome in larger ones. Column large, long, slightly enlarging at calyx 

 and passing into long, nearly uniform columnals a short distance below; in a 

 small specimen of average size, not figured, it is 170 mm. long, with almost 

 uniform columnals about as long as wide throughout its entire length below the 

 upper 25 mm. 



This species is readily distinguished from the other Lower Burlington Taxocrinus by 

 its perfectly smooth surface and rapidly tapering arms ; less easily in superficial appearance 

 from T. ramulosus of the Upper Burlington, especially in young specimens with the inter- 

 brachials little developed; that, however, is of a decidedly shorter habitus, having usually 

 3 IIBr, and its interbrachial system is much farther advanced. T. juvenis,. though generally 

 of an elongate tendency, shows some variation in the number of lower brachials, some speci- 

 mens having 3 IIBr in part of the rays, and one (fig. 9) has only 2 IBr all around. It is 

 characteristically a small-sized species. I have twelve specimens, averaging about like those 

 of figures 3-9. Figure 10 shows an extremely mature specimen, as indicated by the crowded 

 condition of the interbrachial areas, and no other nearly so large has been seen. The specimen 

 figured no, b is an interesting example of the modification of shape caused by accidents in 

 f ossilization ; from figure 11a alone one would suppose, as I did, that with so very short and 

 broad a calyx it must belong to a different species from the elongate forms accompanying it ; 

 but I found that this was mainly due to accidental expansion caused by pressure of a large 

 stem fragment which has pushed in the entire opposite calyx wall, as shown in figure 116. 

 The originals of figures 10 and n are much weathered, and the patelloid sutures to a large 

 extent obliterated. 



In the Memoirs of the American Museum of Natural History, volume 1, part 1, being a 

 " Republication of descriptions of Lower Carboniferous Crinoidea from the Hall collection 

 in the American Museum, with illustrations of the original type specimens not heretofore 



