662 THE CRINOIDEA CAMERATA OF NORTH AMERICA. 
smaller than the corresponding plates of the other sides, and placed at 
a higher level than the middle one. The plates surrounding the anal opening 
not projecting; the opening low down, and directed laterally. 
Horizon and Locality. — Upper Burlington limestone; Burlington, Iowa. 
Type in the Museum of Comparative Zodlogy. 
ftemarks.— This species differs from all others of this group in the abrupt 
spreading of the lower brachials, and the quinquelobate outline of the calyx. 
The nodes upon the basals, although quite distinct in the type, are in other 
specimens but faintly represented, and sometimes absent altogether. 
Platycrinus Halli Sxvum. 
Plate LX XII. Figs. Ga, b, and 7a, b. 
1865. Suumarp; Catal. Paleeoz. Foss. North Amer., p. 388 (Trans. Acad. Sci., St. Louis, Vol. IT.). 
1873. Merx and Wortuen; Geol. Rep. Illinois, Vol. V., p. 454, Plate 3, Figs. 3a, 0, ¢, d. 
Syn. P. planus Hatt (not O. and Suvum.); Geol. Rep. Iowa, Vol. I., Part IL, Plate 8, Figs. 6a, &. 
Syn. P. olla Hatt, 1861 (not Dz Konincx and Lemon 18538); Descr. New Spec. Crin., p. 16. 
A rather large species; the calyx large in proportion to the length of 
the arms, one fifth higher than wide; height of the ventral disk, as compared 
with that of the dorsal cup, as two to three, the former hemispherical, the 
latter bell-shaped, widest around the facets. Plates of the dorsal cup slightly’ 
convex, thickened below the facets, and rather heavy throughout; inter- 
radial sutures somewhat depressed, giving to the cup a slightly pentangular 
outline. 
Height of base equal to half the length of the radials, the outer surface 
regularly rounded, except beneath the column, which rests within a circular 
depression ; sutures between the plates often visible. Radials a little longer 
than wide, slightly spreading, somewhat irregular in form, especially the 
posterior ones, which are frequently wider than the others and asymmetvri- 
cal, owing to the wider and deeper truncation of the upper angles at the 
anal side. Facets rather wide and deep, semicircular to semiovoid, the upper 
edges slightly notched. Costals irregularly pentagonal with concave upper 
faces; rarely trigonal, Distichals, palmars and post-palmars from once and 
a half to twice as wide as long; the distichals of the same ray in sutural 
contact laterally, but among the palmars and post-palmars only the plates 
of the same subdivisions. Arms seven to eight to the ray, quite short. and 
moderately heavy, their two or three proximal plates cuneate and alternately 
arranged, the succeeding ones arranged biserially ; the latter rather long, | 
