BATOCRINIDZ. oll 
Agaricocrinus brevis (Hatt). 
Plate XXX VILL, Figs. 2a-e. 
1858. Actinocrinus brevis— Haut; Geol. Rep. Iowa, Vol. I., Part IL., p. 567, Plate 10, Figs. 3a, 0. 
1881. <Agaricocrinus brevis — W. and Sp.; Revision Paleoer., Part IL, p. 112. 
Syn. Actinocrinus corniculus — Haut, 1858, Geol. Rep. Iowa, Vol. L., Part IL, p. 566, Plate 10, 
Figs. la, 8, ¢. 
A small and delicate species. Calyx wider than high; dorsal cup and 
tegmen of the same height. The lower part of the dorsal cup to the top of 
the radials slightly concave, thence spreading rather abruptly to the arm 
bases; the interradial spaces slightly depressed and somewhat contracted at 
the arm regions. All plates below the arm regions thickened, and rising 
above the suture lines in nodose or tuberculous extensions, with short, incon- 
spicuous ridges reaching to the sides of the plates, where they meet with 
the ridges from adjoining plates. 
Basals small, forming the bottom of the column depression. Radials 
a little longer than wide, their ridges occupying only the upper end of the 
plates, the convex lower part being perfectly smooth. First costals small, 
quadrangular, the sides convex; the second pentangular, shorter than the 
first but wider. JDistichals 2 X 2, very short, supporting the arms. Arm 
facets large, subcircular; the ambulacral openings larger than usual in this 
genus. Arms ten, heavy, slightly increasing in thickness to half their height, 
then tapering gradually, and ending ina sharp point. First interbrachials 
large, nearly as wide as long, rising to the top of the first distichals; the two 
plates of the second-row very narrow, three times as long as wide. First 
anal plate a little narrower than the radials; the three plates above, which 
are almost as large as the corresponding single plate of the four regular 
sides, are followed by four or five small pieces, and these by numerous rows 
of still smaller ones, which form a ridge, with a well defined groove at the 
sides. Ventral disk comparatively short, hemispherical, with a large plate 
in the centre. This plate, which represents the posterior oral, and is almost 
as large as three of the other orals, is surrounded by eight slightly convex 
plates, four of them orals, two overlying the posterior ambulacra, and two 
the anal side. The radial dome plates, which are so prominent in other 
species, either are unrepresented, or cannot be distinguished from the inter- 
ambulacral pieces, which are of moderate size, and only sufficiently tumid to 
bring out distinctly the suture lines. Anus directed laterally, located half 
way between the arm openings and the summit of the posterior oral. 
