194 THE CRINOIDEA CAMERATA OF NORTH AMERICA. 



the second about as large as the first. Distichals four in the calyx, the rows 

 separated by from one to three interdistichals. The second distichal bears 

 a pinnule, which is for the most part incorporated into the calyx. Arms 

 unknown. Interbrachial spaces deeply depressed, so as to give to the calyx 

 at the arm bases a decidedly lobed appearance ; the first plate nearly as 

 large as the radials, the two of the second row slightly smaller, followed by 

 much smaller ones in the third and fourth rows. Anal interradius consider- 

 ably wider, more depressed, and longitudinally divided by a row of elongate, 

 hexagonal anal plates, which form a conspicuous, rounded ridge reaching to 

 the anal opening. The plates at each side of the ridge consist of about the 

 same number, and are arranged in a similar manner as the interbrachials of 

 the four other sides. Anal opening subcentral, in the middle of a small pro- 

 jection. Ventral disk depressed. Orals pushed to the anterior side; four of 

 them much smaller, and arranged in a slightly curving row around the 

 posterior one, which rests against the anal protuberance. Covering pieces 

 of the ambulacra exposed at the surface ; they consist of two series of very 

 short transverse pieces, alternately arranged, forming highly elevated ridges, 

 which gradually decrease in width as they approach the arms. Interambu- 

 lacral plates continuous with the interbrachials ; they are small, irregular, and 

 form deep depressions upon the surface, which contrast strongly with the 

 elevations along the ambulacra. Column round ; axial canal above medium 

 size ; the outer edge of the top joint beautifully crenulated. 



Horizon and Locality. — Niagara group ; Waldron and Hartsville, Ind., 

 and Kacine, Wise. 



Types in the American Museum of Natural History, New York. 



Thysanocrinus occidentalis Hall. 

 Plate XVII I. Figs, 5a, &, c. 



1863. Glyptaster occidentalis — Hall; Trans. Alb. Inst., Yol. lY., p. 204 (Abstr. p. 10); also 28tli Rep. 



N. York State Mus. Nat. Hist. (ed. 2.), 1879, p. 133, Plate 13, Eigs. 7-11; also 11th Rep. 



Geol. Surv. Indiana, 1881, p. 262, Plate 12, Pigs. 7-11. 

 1881. Gli/ptaster occidentalis — W. and Sp. ; Revision Palseocr., Part II., p. 196. 



A somewhat larger species than the preceding. Calyx broadly sub- 

 turbinate, abruptly spreading from the infrabasals; sides slightly convex; 

 plates thin. The brachials of the calyx have on their outer or dorsal surface 

 a prominent rounded ridge, covered by indistinct longitudinal strias, and 

 their inner or ventral side has a deep, semi-circular groove. From both 



