TAXOCRINIDAE 397 



Taxocrinus ungula Miller and Gurley 

 Plate LV, figs, i-io 



Taxocrinus ungula Miller and Gurley, Bull. 8, Illinois St. Mus. Nat Hist., 1896, p. 59, pi. 5, figs. 1, 2. 



A large species. Crown short, broad, turbinate, widely spreading to 

 fourth bifurcation, with rays very conspicuous; height to width 1 to 1. Calyx 

 obconical, with nearly straight sides; height to width at I Ax, 1 to 2; spread 

 from base, i to 2.4. Rays and their divisions deeply convex and prominent, 

 usually diminishing markedly at the IIIBr, and bifurcating by wide angles, 

 like the claws of a bird; beyond this the arms are strong, tapering slowly, and 

 with rather long divisions; sutures strongly arcuate. iBr numerous, spaces 

 wide and depressed. Surface smooth. Dimensions of crown in large mature 

 specimen: height, 54 mm.; width, 48 mm.; base, 15 -mm. ; in young specimen: 

 height, 10 mm. ; width, 13; base, 3. 



IBB very low, forming a flat ring like a thickened columnal; without 



salient angles visible externally. BB of good size, with acute angles; post. B 



large and broad, with large socket on right shoulder for first anal plate. RR 



and IBr not markedly differing in size, diminishing slightly upward, about 



twice as wide as long. IBr 3; IIBr 3, almost as large as the preceding; IIIBr 



about 4 and 6, of even size, two-thirds as large as IIBr and over twice as large 



as the plates following, with little diminution in the next succeeding division. 



Anal tube large and long, the plates rather shorter than wide, and bordered 



with coarsely plated perisome which at the bottom may resemble regular inter- 



brachials; first plate often wide, encroaching somewhat on r. post. R. iBr 



strong and profusely developed to the upper IIBr, with crescentic distal margin, 



and wide areas depressed below level of the rays; similar and successively 



smaller plated areas occur in the second and third axils, separating the brachial 



divisions by wide angles. Column large, flush with the base; proximal 



columnals extremely thin, diminishing in diameter slowly until they alternate 



with longer ones. 



The claw-like appearance of the rays is a marked and constant character of this fine 

 species, by which it can be recognized from imperfect fragments. The form is a further 

 development of the habitus of T. ramulosus, of which it may well be the lineal descendant. 

 It is remarkably constant in all its characters, as shown by a magnificent series of 17 finely 

 preserved specimens, varying from maximum adults upwards of 50 mm. in height and width 

 to the young of only 10 mm. in height in which the turbinate form is equally conspicuous. 

 The contrast with T. colletti in this respect is well shown by a young specimen on Plate LV, 

 figure 11. There is practically no variation in the number of IIBr; in the sixteen specimens 

 144 rami are visible, and of these only five have more than 3 IIBr. Figures 6 and 7 of 

 Plate LV show the only variations observed, being the less conspicuous diminution of the 

 arms at the IIIBr, and greater elongation of these plates. The increase of interbrachials 

 from the young to adult stage is well shown by these specimens. 



