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PLATYCRINID&. 671 
Platycrinus Pratteni WorrtuHen. 
Plate LXX. Figs. 11, 12. 
1860. WortuHen; Trans. Acad. Sci. St. Louis, Vol. I., p. 569. 
1881. W.and Sp.; Revision, Part II., p. 74 (Proceed. Acad. Nat. Sci. Phila. p. 248). 
Syn. P. planus (in part) — Owen and Suumarp; U.S. Geol. Rep. of Minn. Iowa and Wisc., p. 
587, Plate 5.4, Fig. 40 (not 4a). Also Mezx and WorrneEn, 1866; Geol. Rep. Illinois, Vol. 
IIL, p. 467, Plate 16, Fig. 6. 
A large species of the type of P. planus. Calyx elongate, very large in 
proportion to the length of the arms. Dorsal cup once and a half as high as 
wide, almost cylindrical along the radials, but rapidly spreading at the basals, 
which form a moderately deep pentangular basin with its upper angles 
slightly curving upwards; the lower margins projecting outward and form- 
ing a conspicuous rim around the edge, which often is twice as wide as the 
column. Plates quite thin and perfectly smooth; the radials slightly thick- 
ened along the median line. 
Height of basal cup almost one half the length of the radials, its upper 
edges very thin, and overlapping the lower edges of the radials; interbasal 
sutures obsolete. Radials about once and a half as long as wide; the sides 
parallel or very slightly constricted at the top and bottom; the lower face 
convex, the upper angles scarcely truncated. The lower faces of the radials 
and the upper faces of the basals in some specimens contain tooth-like pro- 
jections fitting into each other like interlocking sutures. Radial facets semi- 
circular, occupying nearly half the width of the plates, and filled completely 
by the costals, which are subtrigonal, with concave upper faces. Arms from 
ten to twelve to the ray, comparatively short, rather thin, and very little 
tapering. The arm plates moderately short and slightly waving. Pinnules 
long and in close contact laterally. Of the ventral disk only the middle 
plate of the first interradial row has been observed, which is comparatively 
small and subtrigonal. ‘The two proximal joints of the column circular. 
Horizon and Locality. — Lower Burlington limestone; Burlington, Iowa. 
Type in the Illinois State collection, Springfield. 
Remarks. — This species was confounded by Owen and Shumard, and 
also by Meek, with P. planus, from which it differs in the larger size, the 
proportionally much smaller and thinner arms, the projecting rim of the 
basal cup, and in the undulated basi-radial suture lines. 
