ACTINOCRIXID^. 



579 



They are closed ventrally by two rows of small, irregular side-pieces, wliicli 

 rest upon the inflected edges of the brachials, and enclose a single row of 

 rather large, cuneate, spinous covering pieces, alternately arranged. The 

 upper angle of the brachials is irregular in position, the side bearing the arm 

 considerably shorter and distinctly sloping, the other one, supporting the 

 next brachial, horizontal. The arms are given off at the sides, the proximal 

 joint resting upon the axillary below, and against the truncated lower fece 

 of the plate above ; they are much smaller than the trunks, biserial, and 

 pmnule-bearing. In all other points the genus resembles Actinocrinus. 



Distnhution. — Known only from America, and here only from the Kin- 

 derhook group and Burlington limestone. 



TyiJe of the genus : Stegamcrinus pentagonus. 



Steganocrinus pentagonus (Hall). 

 Plate LXI. Figs. 3a to e ; and 4a, b. 



1858. Aetinommts pentagomts — Hall; Geol. Rep, Iowa, Yol. I., Part II., p. 577,Plate 10, Fifs. (,a,b. 



1866. Steganocrinus pentai/ou-us — 'i.iE^^mi'WowiRY^Ts; Geol Rep. Illinois, Vol. II., p. 196. 



1868. Steganocrinus pentagonus — Meek and Wohtheh ; ibid-, Yol. III., p. 474, Plate 16, Eg. 8. 



1881. Steganocrinus pentagomis — W. and Sp. ; Revision Palffiocr , Part II., p. 151. 



Calyx of medium size, wider than high, distinctly pentangular in its 

 dorsal and ventral aspect. Dorsal cup nearly twice as high as the tegmen, 

 its sides slightly convex to the top of the first costals, the second costals and 

 distichals bent abruptly outward, the latter to a horizontal position, forming 

 five calycine extensions, which bifurcate from the second costals into two 

 free trunks, which bear arms alternately from each side. Plates of the cup 

 thin and but very little convex ; their surfaces marked by radiating ridges, 

 which meet in the centre of the plates, where they form small nodes. The 

 ridges are in single series, except between the radials and basals, where 

 there are two. 



Basals rather small, forming a short, rapidly spreading cup withoiit pro- 

 jecting marginal rim ; the suture lines slightly grooved. Radials and first 

 costals proportionally large, about as long as wide, the latter a little the 

 smaller, and their sides inflected at the upper end to receive the second 

 costals, which are small and distinctly rounded on the back. Distichals 2X2, 

 connected laterally, about half the size of the upper costals, and twice as 

 wide as long, each giving off an arm laterally, one from the one side, the 



