468 THE CEINOIDEA CAMEEATA OF NORTH ABIEEICA. 



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 iuterbrachials ; 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. 



HemarJcs. — " Adinocrimis " trinodus Hall is an abnormal form of this 

 species, the radial dome plates of the two posterior rays, as in the case 

 of " Actinocrinus " tricornis, are produced into spines. In the Revision, 

 Part II., we erroneously placed this form under " Dorycrinus" symnidricus. 



Dorycrinus unicornis (0. and Shum.). 

 Plate XLV. Figs. 8a-e, 9, 10. 



1850. Actinocrinus unicornis — Owen and SnuMAED ; Journ. Acad. Nat. Soi. Pliila., Vol. H. (newser.), 



p. 67, Plate 7, Fig. 12; 1852, U. s! Geol. SurT. Wise, Iowa and Jliun., p. 593, Plate 5A, 



Pigs. 12«, *. 



1858. Actinocrinus unicornis — UxLh; Geol. Pep. Iowa, Vol. I., Pavt II., p. 568, Plate 10, Pigs. 5«, 4, c. 



1873. Dorycrinus micornis — UE-ES. and Woethek ; Geol. Rep. Illinois, Vol. Y., p. 3S0, Plate 6, Pigs. 



2ff, b, c. 

 ,1881. Dorycrinus unicornis — W. and Sp. ; Revision Palffiocr., Part II., p. ISO. 

 1890. Dori/crinus unicornis — S. A. Millee ; North Amer. Geol. and Palajont., p. 2il, Fig. 294. 

 Syn. Actinocrinus tricornis — H.iLL; 1858, Geol. Rep. Iowa, Vol. I., Part II., p. 569. 

 Sju. Dorycrinus tricornis — WmTFiSLS, 1893, Mem. Am. Mus. Nat. Hist. New lork, p. 19, Plate 



n., Figs. 6 to 8. 

 Syn. Adinocrimis pendens -'Sl-ul; 1860, Suppl. Geol. Rep. Iowa, p. 31. 

 Syn. Dori/crimis pendens — W-a\T-!U.i.ii; 1893, Mem. Am, Mus. Nat. Hist. N. York, p. 13, Plate 2, 



Pig. 8. 

 Syn. Dorycrinus lineatus S. A. Millee; 1881, Journ. Cinciii. Soc. Nat. Hist. (December), Plate 7, 



Figs. 3, Ztt. 

 Syn. Dorycrinus infatus Rowlet and Haee ; 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 co?:tals, 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 ; 



