176 THE CRINOIDEA CAMERATA OF NORTH AMERICA. 



RETEOCRINUS Billings. 



1859. E. Billings ; Geo!. Rep. Canada, Decade VI., p. 63. 



1881. W. and Sp. ; Revision Palseocr., Part II., p. 191 (Proceed. Acad. Nat. Sci. Pliila., p. 365). 



1883. P. H. Caepenter; Phil. Trans. Royal Soc. (Part III.), pp. 929-932. 



1883. W. and Sp. ; Amer. Journ. Sci. and Arts, Yol. XXV., pp. 255-268. 



1883. S. A. Miller; ibid., pp. 105 to 113. 



1885. W. and Sp. ; Revision Palseocr., Part III., p. 87 (Proceed. Acad. Nat. Sci. Pliila., p. 309). 



1889. S. A. Miller; North Amer. Geol. and Palajont., p. 277. 



Syn. Ghjptocrinus (in part) — Hall; 1872, 24th Rep. N. York State Cab. Nat. Hist., p. 206, Plate 

 5, Pigs. 18 & 19. 



Syn. Qlyptocrinus (in part) — Wetherby; Journ. Cincin. Soc. Nat. Hist., Vol. II., Plate 16, Pig. 1. 



Syn. Qlyptocrinus (in part) — S. A. Miller; 1881, Journ. Cincin. Soc. Nat. Hist., Vol. IV, p. 83, 

 Plate I, Pig. 5, and 1881, ibid. Vol. VI., p. 227. 



Syn. Gaurocrinus (in part) — S. A. Miller; 1883, ibid. Vol. VI., pp. 228, 229. 



Calyx obconical, its symmetry decidedly bilateral, iiiterradial and inter- 

 distichal spaces profoundly depressed; the plates all along the rays distinctly 

 folded, so as to produce strong, rounded ridges upon their outer surfaces, 

 and deep grooves at the inner. The ridges branch upon the axillaries, and 

 follow the distichals to the arms. Other branches proceed from the middle 

 of the radials to adjoining basals. 



Infrabasals five, variable in size ; sometimes barely protruding beyond 

 the column. Basals ^we, large, protuberant, hexagonal, the upper angles 

 truncated, and the ends somewhat inflected to meet the deep depressions of 

 the interradial spaces. Radials separated all around, sharply angular at the 

 lower faces. Costals two to three; their axillaries closely resembling the 

 radials, but angular above instead of below. Distichals numerous ; all, or 

 nearly all of them, take part in the calyx, and the upper ones retain the 

 form of free arm joints. The proximal pinnule occurs on the second dis- 

 tichal. Arms ten at their origin, but generally bifurcating; composed of 

 rectangular or slightly cuneate pieces. The interradial and interdistichal 

 spaces filled by primary and secondary plates ; the latter very minute, inde- 

 finitely arranged, ill-formed, and interposed between the others, and along 

 the sides of the basals, radials, and brachials. The anal interradius wider, and 

 longitudinally divided into two equal parts by a row of very prominent anal 

 plates, which lie in a straight line from the basals to the anal opening. 

 Ventral disk depressed convex, composed throughout of minute irregular 

 pieces, which form a continuation from the interbrachials and interdistichals. 

 Ambulacra subtegminal. Anal opening excentric, at the top of a small 

 protuberance. 



Column large, pentagonal ; the axial canal of medium size. 



