HEXACEINID^. 761 



densely covered by small granules arranged in rows, some of wliicli 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. 

 Eadials 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 

 bifurcating 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 Meek and Woethen. 

 PlaU LXXVI. Figs. 4a, h, c. 



1869. Meek and Woethen ; Proceed. Acad. Nat. Sci. Pliila., p. 69. 



1873. Meek and Worthen; Geol. Rep. Illinois, Vol. V., p. i40, Plate 3, Figs. Iff, b, c. 



1881. W. and Sp.; Revision Pateocr., Part XL, p. 81. 



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 ridge.s, 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 



