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708 THE CRINOIDEA CAMERATA OF NORTH AMERICA. 
Platycrinus Yandelli, var. perasper Suvum. 
Plate LX VIL. Figs. 4a, b. 
SG5.- 2 en eae Catal. Paleoz. Foss. of North Amer., p. 389. 
1881. P. perasper —W. and Sp.; Revision, Part IL., p. 73 (Proceed. Acad. Nat. Sci. Phila., p. 247). 
Syn. P. nodobrachiatus Hatt, 1861 (not 1858); Descr. New Spec. of Crin., p. 17. 
In the form of the dorsal cup, the proportions of its plates, and the size 
of the arms, closely resembling P. Fandellz, but the nodes covering the sur- 
face much more numerous; they are placed close together without being 
confluent, are very prominent, and cover the dorsal surface of the arms. 
Those upon the brachials to the last axillary, although smaller, are equally 
well defined, and are arranged transversely in two rows of from four to five 
nodes to each row, those upon the biserial arm plates in only one row. The 
latter are more or less confluent, and form an undulated ridge at the upper 
edge of the plates, which gives to the transverse sutures a waving outline. 
This variety generally has six arms to the ray, which are slightly flattened 
on the back and obscurely grooved along the median line. The stem twists 
rapidly, and is composed at its proximal end of short elliptic joints. 
Horizon and Locality. — Lower Burlington limestone, Burlington, Iowa. — 
Type in the Museum of Comparative Zodlogy. 
Platycrinus spinifer W. and Sp. (nov. spec.). 
Plate LX VI. Fig. 7. 
Closely resembling P. Vandelli, but somewhat larger. Dorsal cup saucer- 
shaped, the basals proportionally large, the radials distinctly curving, their 
facets projecting outward. Plates thin, covered with large, rather sharp 
nodes, placed in concentric lines parallel to their margins; there being gen- 
erally three such lines upon the basals, and two or three upon the radials, 
the latter arranged so as to form a diagonal line from the facet to each 
lower angle of the plates. Similar nodes, but somewhat smaller, cover the 
arms, every plate above the costals having three nodes — the costals four to 
five — transversely arranged, and occupying the median line of the plates; 
sometimes, however, in the upper part of the arms, the nodes become 
confluent and form undulated ridges. 
Basals large, slightly convex except the middle part, which is abruptly 
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