494 THE CRINOIDEA CAMERATA OF NORTH AMERICA. 
cavity is formed by the basals, radials, and the lower portions of the first 
interbrachials, which are stretched out horizontally, and form the flat bottom ; 
the first costals constitute the sides, while the second costals and the upper 
portions of the interbrachials deflect outward and slightly upward, and form 
the rim upon which the calyx rests; the latter plates are a little convex, 
those within the convexity are flat. Suture lines well defined, 
Basals concealed by the column.  Radials nearly as long as wide, the 
lower margins deflected to form the columnar depression, First costals 
quadrangular, nearly twice as wide as long, bending abruptly upwards on 
their lower margins; the second larger and throughout wider than the first, 
often larger even than the radials. First distichals quite variable, in some 
specimens almost twice as large as in others ; they are succeeded by a single 
cuneate plate, or by two pieces, the edge of the one overlapping the other. 
Arms ten; contiguous to the third plate above the axillary; stout, but 
shorter than in any of the preceding species, First interbrachials sub- 
ovate, very large, sometimes twice as large as the radials; they rise to 
the middle of the first distichals, where they are followed by two long, 
very narrow pieces, which reach up to the level of the arm openings. 
The first anal, which is narrower and higher than the radials, supports 
three large plates, the middle one narrower than the two outer, and there 
are three others in the next range. Posterior oral somewhat excentric, 
leaning to the posterior side, very large and strongly nodose; it is sur- 
rounded by nine or ten plates consisting of the smaller orals, which are less 
tumid and of but half its size, two somewhat smaller radial plates, and three 
to four small, almost flat, supplementary anal pieces. The radial plates near 
the outer margin of the disk are somewhat larger than the smaller orals. 
Interambulacral plates not numerous, there being rarely more than five to 
each side. Anal area wide and flat; the anus placed midway between the 
arm regions and the summit of the posterior ‘oral; the opening directed 
laterally. Column very small compared with the size of the species; joints 
of almost uniform width; axial canal pentangular. 
Horizon and Locality. — Upper Burlington limestone ; Burlington, Iowa, 
and at the same horizon in Illinois and Missouri, 
Type in the Illinois State collection at Springfield. 
Remarks. — This species resembles A. Wortheni Hall, in general outlines, 
and has a similar flattened anal area, but the latter is a much larger species, 
