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488 THE CRINOIDEA CAMERATA OF NORTH AMERICA. 
Agaricocrinus Americanus (Rormer). 
Plate XLII. Figs. 1, 2a, b. 
1855. <Amphoracrinus americanus —Rozmur; Lethea Geogn. (Ausg. 3), p. 250, Plate IV., Figs. 15a, 0. 
1865. Agaricocrinus americanus —SuumMaRD; Trans. Acad. Sci., St. Louis, Vol. II., p. 351. 
1881. <Agaricocrinus americanus — W. and Sp.; Revision Paleocer., Part II., p. 111. 
(Not Amphoracrinus americanus QuunsteDt, Handb. der Petrefactenkunde [Aufl. 3], p. 957, Plate 77, 
Fig. 7, = Agaricocrinus Wortheni Hall.) 
Syn. Agaricocrinus dissimilis 8. A. Mitten; Adv. Sheets 17th Rep. Geol. Survey Indiana, p. 55, 
Plate 8, Fig, 11. 
Calyx hemispherical, more or less deeply excavated at the bottom. The 
upper half of the interbrachials and the arm facets are the only parts of the 
dorsal cup visible from a side view; the basals, radials, and costals occupy 
the basal concavity, and the distichals and palmars stand more or less at 
right angles to the vertical axis of the calyx. All plates of the dorsal cup 
show a slight tendency to become convex, and the suture lines are moder- 
ately distinct. 
Basals very small, and covered completely by the upper stem joint. 
Radials small, very little larger than the first costals; their extreme lower 
edges bending abruptly mward to form the concave base. First costals 
quadrangular with convex sides. Second costals and first distichals larger 
than the radials, and their surface generally somewhat more convex than 
that of the plates below. The first distichal of the three anterior rays, in 
which there are two arms, is followed by a cuneate second, which interlocks 
with the first, and with the three lower arm plates of the inner rows. In 
the two posterior rays, which have three arms— exceptionally four — the 
divisions next to the anal side have but one distichal and two palmars. 
Arms heavy at the base, but tapering all the way up to the tips, where they 
end in a sharp point. They are composed of two rows of short joints, with 
slightly convex outer faces, which give off rather stout and long pinnules. 
Interradial spaces somewhat depressed at the arm bases; the anal side very 
much the widest. First anal plate longer than the radials, and longer than 
wide; it is followed by a second anal and two interbrachials, one at each 
side, the latter rising almost to a level with the arm bases, and beyond the 
upper end of the second anal. The next row generally consists of two short 
plates, which are succeeded by numerous small, irregularly arranged, convex 
pieces, which form a large, abruptly protruding lateral anal protuberance, 
with the opening in the middle. First interbrachial of the regular sides 
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