244 THE CRINOIDEA CAMERATA OF NORTH AMERICA. 
as the costals; the two upper shorter and free. There are four arms to each 
arm opening, the upper bifurcation taking place from the third plate. Arms 
rather stout and long for the genus; they are erect, biserial from the last 
axillary, and have closely set pinnules. Calycine appendages small and short ; 
directed outward, almost at right angles to the calyx. They are composed 
of single joints, of which the four or five proximal ones of adjoining rays are 
truncated laterally on apposed sides, and connected with one another by 
rigid suture; the plates interlocking. After separating, the two tubes taper 
rapidly, and terminate at the end of the fourth or fifth joint. The number 
and arrangement of the interradial plates is quite variable ; but in the major- 
ity of specimens the plate between the radials is succeeded by three plates ; 
some, however, have but two, except at the anal side which always has 
three ; there are two or three in the next row, exceptionally four at the anal 
side. Interdistichals five to six. Ventral disk low-convex, with well defined 
interradial pits; the posterior one larger, and containing the anus. Column 
round; axial canal sharply stellate. 
Horizon and Locality. — Upper Burlington limestone; Burlington, Iowa. 
Type in the Museum of Comparative Zoblogy, Cambridge. 
Remarks. — Readily distinguished by the upright arms, and short, rapidly 
tapering tubes. 
Gilbertsocrinus reticulatus (Harr). 
Plate XVII. Figs. 1a, 6. 
1860. Zrematocrinus reticulatus —Hatt; Descr. New Spee. Crin., p. 9; bis Boston Journ. Nat. Hist., 
Vol. VII., p. 325. 
1881. Ollacrinus reticulatus — W. and Sr.; Revision Paleocr., Part IT., p. 219. 
1889. Goniasteroidocrinus reticulatus —S. A. Mitten; North Amer. Geol. and Paleont., p. 250. 
Calyx small compared with the preceding species, about as wide as high ; 
dorsal cup urn-shaped with convex sides and a wide and deep concavity 
at the bottom; ventral disk almost flat. Plates slightly convex, their sur- 
faces marked by a series of obscure ridges, radiating from the centre of the 
plates to adjoining ones. The ridges follow the rays, and those passing 
from the radials to the basals are stronger and somewhat higher; the latter 
producing around the basal concavity at the bottom of the calyx the well 
defined figure of a pentagon with convex sides. 
Infrabasals forming a pentangular disk, of which the angles project quite 
plainly beyond the column. Basals large, their upper ends curving abruptly 
upwards, the lower portions of the plates to two thirds their length, together 
