produce depressions at the interradial spaces. Bottom of the dorsal cup 
deeply excavated to the middle of the second costals, the distichals thus 
forming the base upon which the calyx rests. All plates within the con- 
cavity are flat ;- while the distichals are more or less convex, and sometimes 
covered with indistinct transverse angularities. 
Basals small, more deeply depressed than the surrounding plates, and 
hidden from view by the column ; the axial canal moderately small and pent- 
angular. Radials more than twice as wide toward the upper end than at the 
{ 
| 
492 THE CRINOIDEA CAMERATA OF NORTH AMERICA. 
lower; the lower margins inflected to form the basal concavity. First costals 
| 
one half wider than long, the upper face wider than the lower; they are i 
quadrangular in outline, although frequently one or both upper angles are | 
slightly truncated by the second interbrachials. Second costals as large as / 
the radials or larger, six to eight-sided. Distichals 2 X 2, twice as long | 
as the arm plates, interlocking with their fellows of the opposite division, | 
and with the arm plates to the third row. Arms two to the ray, long, 
very heavy in the lower portions, but gradually tapering until quite thin 
toward the extremities. Interbrachials three ; the first comparatively short, 
often not reaching the top of the first costals; the two succeeding ones un- 
usually long and extremely narrow, rising from within the basal concavity to | 
a level with the arm bases; these plates support three elongate, moderately | 
| 
large interambulacrals, which are followed by six to eight smaller ones. First 
anal higher than the brachials; supporting on its sloping upper sides two 
rather large interbrachials, and on the middle face an elongate anal piece ; 
the next row generally consists of four plates, which rise to the height of 
ay | the arm bases. Ventral disk depressed pyramidal in its anterior aspect, the 
i (ee posterior side greatly protruding outward and upward, and formed into a 
El large anal process, which rises beyond the top of the posterior oral, and from 
| a 4 to 6 mm..above the plane of the ventral disk. It is narrower at the base 
in | than at the upper end, and somewhat depressed around the anus, which 
Me ‘ opens obliquely upwards. Orals and radial dome plates large and tuber- 
Gi | culous ; the former in contact laterally; the latter separated from one an- 
te | | other, and from the orals, by small perisomic plates. Column small for the 
size of the species. 
Horizon and Locatity.— Uppermost part of the Upper Burlington lime- 
stone; Burlington, Augusta, and Pleasant Grove, Iowa. 
Remarks. — This species is readily distinguished from A. americanus by 
the very different size, form, and arrangement of its interbrachial plates, 
renee + nonsense 
7 Se 
Ce 
| 
4 
