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PLATYCRINID&. 691 
small, slightly projecting near the arm bases. The interambulacral spaces 
are formed of five plates, of which the middle one of the first row is twice 
as large as the others, and hexagonal. The two or three upper stem joints 
circular, the succeeding ones elliptic. | 
Florizon and Locality. — Upper Burlington limestone ; Burlington, Iowa. 
Type in the Museum of Comparative Zodlogy. 
SCULPTUS GROUP. 
Basals and radials forming a deep cup; the base high and distinctly con- 
vex ; the plates ornamented by transverse lines of confluent nodes following 
the margins of the plates. Radial facets small; arms moderately large. 
Platycrinus sculptus Hatt. 
Plate LX VILL. Fig. 5, and Plate LXXV. Fig. 8, 9. 
1858. Hatn; Geol. Rep. Iowa, Vol. I., Part II., p. 536, Plate 8, Fig. 11. 
1881. W. and Sp.; Revision, Part II., p. 75 (Proceed. Acad. Nat. Sci. Phila., p. 249). 
Syn. Platycrinus rotundus 8. A. Mituer; Geol. Surv. Missouri, Bull. 4, p. 20, Plate 2, Figs. 11 
and 12. 
Dorsal cup of medium size, in very mature specimens higher than wide, 
a little wider than high in small ones, growing proportionally higher with age; 
the sides evenly convex from the stem upwards. Surface of plates orna- 
mented with rows of confluent nodes or undulated ridges, the base being 
covered by three to five rows, running parallel to the upper margins of the 
plate ; five others radiate from the column to the upper angles. Similar 
rows, varying from three to six, according to the age of the specimen, fel- 
low the margins of the radials, and three rows proceed from the facets to 
the lower face; two of these directed diagonally to the outer angles, the 
middle one, which is sometimes unrepresented, placed vertically. 
Base from one fourth to one third as high as the dorsal cup, basin- 
shaped ; the median portions slightly truncated and a little excavated; the 
upper margins of the plate somewhat beveled, giving to the basi-radial 
sutures a slight depression. Radials quadrangular, the lower edge convex, 
the sides very slightly spreading, the upper face but little sloping to the 
angles. Facets small, semicircular, directed obliquely upwards, occupying 
but one third the width of the plates, and only a small portion of their 
height. Costals small, trigonal, sometimes narrower than the facets, so that 
portions of the first distichals come in contact with the radials. First dis- 
