THE CRINOIDEA CAMERATA OF NORTH AMERICA. 
Oo 
bo 
io 2) 
Hadrocrinus discus Lyon. 
Plate XXIV., Fig. 1. 
1869. Lyon; Trans. Amer. Philos. Soe., Vol. XIII., p. 448, Plate 26, fig. a. 
1881. W.and Sp.; Revision Paleocr., Part II., p. 222. 
A very large species. Dorsal cup flat-saucer-shaped, the radials forming 
a shallow concavity, of which the basals occupy the bottom, the radials the 
sides. From the top of the radials to the second distichals the plates are 
directed horizontally, and from there they proceed slightly upward to near 
the arm bases, where they attain again a horizontal position. Plates moder- 
ately heavy, apparently without ornamentation; slightly concave, the median 
space having a shallow circular pit, sometimes two being placed close to- 
gether. Basals not visible in the specimens, and judging from the space 
assigned to them, they were unusually small. Radials and costals small in 
proportion; the former a little the larger, their lower faces one half the 
width of the upper; the upper stoping faces larger than the corresponding 
lower ones. Second costals almost regularly pentagonal. Distichals 2 X 10, 
larger than the radials, considerably longer than wide; the first hexagonal, 
the second pentagonal and axillary. Palmars 4 X 20 in the calyx, the two 
lower ones as large as the distichals and of a similar form, the two upper 
much shorter and slightly curved for the reception of the arms. Inter- 
brachials nine or more, irregularly arranged, all nearly equal and as large as 
the distichals. The anal interradius has three plates in the second row, which 
are narrower than the two of the other sides. Interdistichals three, longi- 
tudinally arranged, elongate, hexagonal, as large as adjoining brachials. 
Structure of arms and ventral disk unknown. Columnar facet large, beauti- 
fully striated. 
Horizon and Locality. — Upper Helderberg group; Falls of the Ohio, 
near Louisville, Ky. 
Types i the Lyon collection. 
Hadrocrinus plenissimus Lyon. 
Plate XXIV., Figs. Za, b. 
1869. Lyon; Trans. Amer. Philos. Soc., Vol. XIII., p. 445, Plate 26, Figs. 1-3. 
1881. W. and Sp.; Revision Paleoer., Part IT., p. 222. 
The specimens are fragmentary and crushed, so as to leave some doubt 
as to the actual form and size of the calyx, except that it was depressed and 
