692 THE CRINOIDEA CAMERATA OF NORTH AMERICA. 
tichals small, twice as wide as long, placed obliquely, the two of the same 
ray connected laterally. Second distichals considerably wider than the first, 
but not longer. Palmars and post-palmars of the form of the distichals, 
but somewhat smaller. Arms eight to the ray; cylindrical, moderately 
strong, biserial from the start; the upper edges of the plates forming a 
small thickened ridge projecting over the lower margin of the succeed- 
i ab tate 
ing plate. Structure of ventral disk unknown. Column small for the size 
of the specimens, elliptical and twisted; the transverse articular ridge of 
apposed faces prominent, with a distinct fossa at each side. 
Horizon and Locality. — Lower Burlington limestone; Burlington, Iowa. 
Type in the (Worthen) Illinois State collection, Springfield. 
Remarks. — The ornamentation in some specimens is more conspicuous 
than in others. The length of the radials and the depth of the basal cup 
are also quite variable. The latter, however, may be understood by consid- 
ering that the rows of nodes surrounding the margins of the plates repre- 
sent lines of growth, and increased in number with age, and as the plates 
grew faster longitudinally than horizontally, they became in the older speci- 
mens proportionally longer. | 
This species, with slight modifications, apparently occurred also at Lake 
Valley, New Mexico. A specimen from that locality (Plate LXVIIL., Fig. 
5) shows the structure of the ventral disk, which had not been observed in 
any from Burlington, but as the arms are not preserved there is some doubt 
as to its specific identity. It agrees with the Burlington specimens perfectly 
in the ornamentation of the plates, but the second joint of the stem is de- 
cidedly elliptic, the radials somewhat more convex, producing slight angular 
depressions at the basi-radial and interradial sutures, the upper angles of the 
plates are more inflected, and the facets apparently a little deeper. The 
ventral disk 1s depressed-hemispherical, decidedly flattened at the top, the 
posterior side somewhat bulging, the orals comparatively small and very 
slightly convex, the covering pieces tuberculous. There are but three inter- 
ambulacral plates to each side, of which the middle one is extremely large, 
and erect except that the upper end curves abruptly inward; those of the 
regular sides are subtrigonal in outline, but actually hexagonal; the anal 
one wider, subquadrangular, and the top slightly excavated to form the 
anal opening, which points upward. 
