PLATYCRINID.ZA. 663 
their upper and lower faces parallel, the outer lateral faces provided with a 
sharp projection placed in front of the pinnules. 
Ventral disk convex, gradually curving to the summit, quinquelobate as 
seen from above, the plates slightly convex. Orals rather asymmetrically 
arranged ; the posterior one larger than the other four, and pushed in be- 
tween them. Ambulacral plates of the first order consisting of but few 
large pieces of rather irregular arrangement, those of the second order 
about one half smaller. Interambulacral plates of the regular sides five 
in two rows; the middle one of the first row large, elongate, hexangular, 
much narrower at the top than at the bottom, and deeply wedged in between 
the radials; the two at the sides very narrow, the edges toward the ambu- 
lacra deeply scalloped by adjoining covering-pieces. Anal side considerably 
larger, the notch between the radials deeper ; the middle plate much shorter, 
wider and pentangular, supporting upon its sloping upper faces two smaller 
pieces, which, being at a higher level, form with their lower faces and with 
the sloping lower sides of the middle plate a sharp angle; the plates of the 
first row are followed by numerous smaller ones, which form a large rounded 
protuberance, containing the anus. Column moderately large; the three 
upper joints circular, the lower ones distinctly elliptic. 
Florizon and Locality. — Upper Burlington limestone; Burlington, Iowa. 
ftemarks. —This species resembles P. pileiformis in the form of the calyx ; 
but the plates are heavier, the arms comparatively shorter, not so heavy, and 
much more numerous. 
Platycrinus acclivus S. A. Mitter. 
1891. 8. A. Minter; Geol. Surv. Missouri, Bull. 4, p. 12, Plate 1, Figs. 9 and 10. 
According to Miller, the dorsal cup somewhat obconoidal, nearly one half 
higher than wide, slightly “angular in the direction of the arms,” sutures 
distinct but not beveled, surface apparently smooth, but the specimen may 
not have preserved the surface ornamentation. Basals form an obconic, sub- 
pentagonal cup, a little wider than high, and truncated below. Radials a 
little longer than wide, very slightly expanding above, and terminating 
in an upward, central prolongation for the reception of the costals. Facets 
facing upward; less than one third the width of the plates, subcircular in 
outline, with the exception of a slight truncation at the inner side, and a 
small concave ambulacral furrow. Column round at the proximal end, “the 
