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468 THE CRINOIDEA CAMERATA OF NORTH AMERICA. 
each side, reaching up to the posterior oral. It is composed of a series 
of four to five anal plates, longitudinally arranged ; the first larger than the 
radials ; the second interposed between two interbrachials; the third occupy- 
ing the arm regions; the upper one followed by numerous irregular, small 
pieces, forming a tumor-like inflation which is pierced by the anus. Posterior 
oral central and drawn out into a long, sharp spine, which sometimes exceeds 
in length the height of the calyx. The other orals are somewhat tumid, as 
also the primary radial dome plates; while the interambulacral plates are 
almost flat. Anus placed at half way between the arm bases and the posterior 
oral, opening out laterally. 
Horizon and Locality. — Lower Burlington limestone; Burlington, Iowa 
(a rare species). 
Type in the University Museum at Ann Arbor. 
fiemarks. —“ Actinocrinus” trinodus Hall is an abnormal form of this 
species, the radial dome plates of the two posterior rays, as in the case 
of “ Actnocrinus”’ tricornis, are produced into spines. In the Revision, 
Part IL., we erroneously placed this form under “ Dorycrinus” symmetricus. 
Dorycrinus unicornis (0. and Suum.). 
Plate XLV. Figs. Sa—e, 9, 10. 
1850. Actinocrinus unicornis— Owxnn and Suvmarp; Journ. Acad. Nat. Sci. Phila., Vol. IT. (new ser.), 
p- 67, Plate 7, Pig. 12; 1852, U. 8. Geol. Surv. Wisc., Iowa and Minn., p. 598, Plate 5.4, 
Figs. 12a, 6. 
1858. Actinocrinus unicornis —Hatt; Geol. Rep. Iowa, Vol. I., Part IL., p. 568, Plate 10, Figs. 5a, 2, ¢. 
1873. Dorycrinus unicorais— Muux and Worruen ; Geol. Rep. Illinois, Vol. V., p. 380, Plate 6, Figs. 
2a, b, ¢ 
1881. Dorycrinus unicornis —W. and Sp.; Revision Paleoer., Part IT., p. 180. 
1890. Dorycrinus unicornis —8. A. Mitter; North Amer. Geol. and Paleont., p. 241, Fig. 294. 
Syn. Actinocrinus tricornis — HauL; 1858, Geol. Rep. Iowa, Vol. I., Part I1., p. 569. 
Syn. Dorycrinus tricornis — WuttFIELD, 1893, Mem. Am. Mus. Nat. Hist. New York, p. 19, Plate 
II., Figs. 6 to 8. 
Syn. Actinocrinus pendens — Hatt; 1860, Suppl. Geol. Rep. Iowa, p. 31. 
Syn. Dorycrinus pendens — WHITFIELD; 1893, Mem. Am. Mus. Nat. Hist. N. York, p. 18, Plate 2, 
Fig. 8. 
“Syn. Doryerinus lineatus 8, A. Mit1mr; 1881, Journ. Cincin. Soc. Nat. Hist. (December), Plate 7, 
Figs. 3, 3a. 
Syn. Dorycrinus inflatus Rowiny and Hare; 1891, Kansas City Scient., p. 114, Plate 3, Fig. 4. 
Calyx spheroidal, broadly truncate at the lower end, moderately spread- 
ing to the top of the costals, thence abruptly to the base of the arms. Ven- 
tral disk almost as high as the dorsal cup, inflated at the posterior side, and 
crowned by a long central spine. Plates of the dorsal cup highly elevated ; 
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