\ 
0 
HEXACRINIDZA. 761 
densely covered by small granules arranged in rows, some of which run from 
the truncated lower part to the upper faces, and a somewhat stronger one to 
each angle; others run parallel to the undulating upper margin. 
Basals large, occupying more than three eighths the height of the calyx. 
Radials variable in form, but always longer than wide, and narrower at the 
upper face than at the lower; their ornamentation is similar to that of the 
basals, consisting of narrow rows of granules passing up and down the plates, 
and others crossing them transversely; facets occupying about one half the 
width of the radials at their upper end, shallow, and directed upwards. Anal 
plate generally wider at the bottom than the radials, and narrower above ; 
the lower faces distinctly angular. Costals two; the first shorter than the 
biturcating second. Arms ten, strong, slightly tapering upward, and biserial. 
Pinnules very long and closely packed; composed of six or seven joints, 
each one about eight times as long as wide. Structure of the ventral disk, 
and form and position of the anus unknown. Column round, the nodal joints 
larger and rounded at their edges, the internodals quite short. 
Horizon and Locality. — Lower Burlington limestone, Burlington, Iowa. 
Dichocrinus lineatus Mrex and WortHen. 
Plate LX XVI, Bigs. Zab, ¢. 
1869. Merrx and WortueEn; Proceed. Acad. Nat. Sci. Phila., p. 69. 
1873. Merxrx and Wortuen; Geol. Rep. Illinois, Vol. V., p. 440, Plate 8, Figs. la, 3, c. 
1881. W. and Sp.; Revision Paleoer., Part II., p. 84. 
A large species, intermediate between D. ovatus and D. pisum, with 
delicate longitudinally striate ornamentation. Calyx pyriform, about as 
wide as high, not rounded at the base as in the former, nor flattened as in 
the latter; it is widest at midway, and contracts but little at the upper end. 
Surface densely and uniformly covered with minute, closely arranged longi- 
tudinal ridges, proceeding in parallel lines from the upper part of the radials 
downward ; those following the median portions of the plates continuous to 
the foot of the basal cup, the outer ones meeting at acute angles with 
corresponding ridges from adjacent radials. On the anal plate, in which the 
upper face is much narrower than the lower, the ridges run parallel to the 
lateral margins of the plate, and meet the inner ridges at acute angles in 
a similar manner to those upon the basals. 
Basal cup conical, with slightly curving sides; its height equal to the 
length of the radials. Basi-radial and interradial sutures rather well defined. 
96 
——S 
