496 THE CRINOIDEA CAMEEATA OF NORTH AMERICA. 



four together ; it is separated from the latter, and these from one another, 

 by rather large supplementary pieces, even in the smallest specimens. Simi- 

 lar plates intervene between the orals and radial dome plates, and pass over 

 the ambulacra. The radial dome plates, which are comparatively small, 

 occupy the margin of the tegmen. 



Horizon and Locality. — Keokuk group, Indian creek, Montgoniery Co., 

 Ind., where large numbers of excellent specimens were obtained. 



Remarks. — The construction of the tegmen is the most characteristic 

 feature of this .species. The isolated orals, protruding anal ridge, and the 

 small radial dome plates, separate it at once from allied forms. The posterior 

 rays occasionally have four arms, but the other raj's never more than two, 

 and on a specimen of this kind Miller's Agaricoerinus Gorhji is based. 



Agaricocrinus Whitfield! Hall. 

 Plate XLII. Fig. 3, and Plate XLIII. Figs. Sa, h. 



1S5S. Hali, ; Geol. Rep. Iowa, Vol. I., Part, II., p. 621. 



1860. Hall; Ibid., Supplement, Plate 3, Kg. 5. 



1873. Meek and Wobthen ; Geol. Rep. Illinois, Vol. T., p. 499, Plate 12, Figs, la, b, and Plate 15, 



Pig. 8. 

 1881. W. and Sp. ; Revision Palffiocr., Part II., p. 113. 



Calyx rather large, depressed subhemispherical ; the dorsal cup deeply 

 concave, so that the lower end of the calyx rests upon the first distichals. 



Basals entirely hidden by the column. Eadials small, wider than long, 

 hexangular. First costals slightly smaller than the radials, quadrangular or 

 pentangular, rarely hexangular ; the second costals varying from pentan- 

 gular to heptangular, and considerably larger than either radials or first 

 costals, especially wider. First distichals very large, of imequal size; the 

 second shortest, and followed hy the biserial arms, except in the posterior 

 rays, in which the divisions next to the anal side have palmars fi'om the first 

 distichals. Arm facets large ; the arm structure unknown. First inter- 

 brachials short, rising generally to the middle of the first costals, but some- 

 times touching the second ; plates of the second row very long and narrow, 

 curving abruptly upward to half the height of the arm facets, where they 

 are followed by still narrower ones, which in part are interambulacral. First 

 anal narrower than the radials; the two plates at the sides of the second 

 anal, which are much longer than the first interbrachials of the other sides, 

 on a level with the lower part of the distichals ; the next row consisting of 



