496 THE CRINOIDEA CAMERATA 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. 
P] 
Horizon and Locality.— Keokuk group, Indian creek, Montgomery Co. 
Ind., where large numbers of excellent specimens were obtained. 
y) 
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 rays never more than two, 
and on a specimen of this kind Miller's Agaricocrinus Gorbyi is based. 
Agaricocrinus Whitfieldi Hatt. 
Plate XLII. Fig. 3, and Plate XLIIT. Pigs. Sa, 6b. 
1858. Hatz; Geol. Rep. Iowa, Vol. I., Part IL, p. 621. 
1860. Hatz; Ibid., Supplement, Plate 3, Fig. 5. 
1873. Merk and WortueEn; Geol. Rep. Illinois, Vol. V., p. 499, Plate 12, Figs. la, 4, and Plate 15, 
1881. W. cee Revision Paleocr., 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. Radials 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 unequal size; the 
second shortest, and followed by the biserial arms, except in the posterior 
rays, in which the divisions next to the anal side have palmars from 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 
