392 THE CRINOIDEA CAMERATA OF NORTH AMERICA. 
rather deeply concave, directed outward. Ampbulacral openings arranged in 
groups, the spaces between the posterior rays wider than those between the 
other rays. Respiratory pores large, arranged in five pairs interradial in 
position. Arms twelve to fourteen, incurving, extremely heavy for the size 
of the species; they are biserial from the second free plate, rounded on the 
back in the lower portions, but flat and spatulate above, reaching a width of 
three times the diameter at the base. In the rounded part, the back of each 
alternate plate in both series is covered by a small node, which does not 
extend to the flattened portions; the arms are keel-shaped, heavy along the 
median line, and knife-like at the edges. Interbrachials three to four in the 
four regular rays; the first large and wider than high; the upper smaller 
and arched by the arm-bearing brachials. At the posterior side the anal is 
followed by three and two pieces. The ventral disk consists of but few 
plates, of which the posterior oral is the largest; it is slightly convex, 
central in position, and bends upward, forming a part of the ventral tube; 
the other orals and radial dome plates are somewhat nodose. Anal tube 
excentric, large at the base, and curving to one side. . 
Horizon and Locality. — Upper Burlington limestone; Burlington, Iowa. 
Types in the collection of Wachsmuth and Springer. 
Eretmocrinus depressus W. and Sp. (noy. spec.). 
Plaie XXXVI. Figs. 11a, b. 
Near Hretmocrinus remibrachiatus, but the proportions of the calyx quite 
different ; the ventral disk comparatively shorter and less bulging; the bot- 
tom of the dorsal cup considerably broader, and the arm openings directed 
obliquely upwards in place of horizontally. The dorsal cup spreads moder- 
ately from the top of the basals to the top of the distichals, thence abruptly 
to the arms; its height is equal to one third its width at the arm bases; the 
rays are indistinctly lobed. The plates vary from almost flat to distinctly 
convex ; they are without ornamentation, and the suture lines are obscure. 
Base extended outward, forming a broad, projecting rim with a sharp 
edge at the lower border; its lower face almost flat, and only one third 
of its width is occupied by the column. Radials comparatively small, a little 
wider and somewhat longer than the costals; the latter quadrangular and 
pentangular. Distichals two, the upper one axillary, giving off from each 
side two short palmars supporting four arms; the anterior ray exceptionally 
