RHODOCRINID.E. 247 
Horizon and Locality. — Lower Burlington limestone ; Burlington, Towa. 
Type in the Museum of Comparative Zodlogy, Cambridge. 
Remarks. — This species is distinguished from G. typus by the form of 
the spines on the basals and radials, the thinness and delicacy as well as the 
folding of the plates, and by the cylindrical form and smoothness of their 
appendages. 
Gilbertsocrinus spinigerus (Hatt). 
Plate XV. Figs. 3a, b, e. 
1862. Trematocrinus spinigerus — Hatt; 15th Rep. N. Y. State Cab. Nat. Hist., p. 128. 
1866. Goniasteroidocrinus spinigerus —MexK and Wortu.; Geol. Surv. Illinois, Vol. H., p. 222. 
1872. Gilbertsocrinus (Irematocrinus) spinigerus — Hatt; New York State Mus. Nat. Hist., Bull. I., Plate 
la, Fig. 9 (privately distributed). 
1877. Goniasteroidocrinus spinigerus —S. A. Mrtter; Cat. Amer. Paloz. Foss., p. 80. 
1881. Ollacrinus spinigerus — W. and Spr. ; Revision Paleocr., Part H., p. 219. 
1889. Goniasteroidocrinus spinigerus —S. A. Mitier ; North Amer. Geol. and Paleont., p. 250. 
A small species. Calyx widest across the radials, somewhat constricted 
at the arm bases, expanding at the upper margin. The rays marked by 
broad, rounded ridges proceeding to the arm openings, and giving to the 
section across the costals a pentangular, and across the distichals a deeagonal 
outline; while the section at the margin of the disk, where the appendages 
meet in pairs, assumes again a pentangular outline, but the angles are inter- 
radial instead of radial. The plates without ornamentation, but the radials, 
first costals and first interradials are extended into sharp nodes or small 
spines. Basal concavity deep and wide, involving the infrabasals, basals, and 
portions of the radials and interradials. 
Infrabasals comparatively large, forming a regular pentagon. Basals 
large ; their upper sloping faces twice as long as the corresponding lower 
ones; broadly truncate above. Radials of nearly the same size as the basals, 
and deeply wedged in between them. First costals considerably larger than 
the second, and but little smaller than the radials. Distichals quite small, 
especially the second, which is deeply excavated to form the arm openings. 
Yalycine tubes confluent at four sides, those facing the anal side simple and 
separated by anal plates. The appendages are short, directed almost horizon- 
tally, and are composed of joints about as long as wide. Arms erect, rather 
stout, the plates cuneate; they start in pairs from the calyx, branch on the 
fifth plate, and again on the eighth. The plates of the interradial spaces 
small, except the first which is very large ; it is followed by 3, 3, 8, 5, and 
two plates. Interdistichals three or more. Ventral disk flat, with deep 
