RHODOCEINIDJE. 239 



Gilbertsocrinus tuberosus (Lyojst and Cass.). 

 Plate XV, Figs, la, h ; Flate XVI. Figs 1 to 6 ; Plate XVII . Fig. 6. 



I860. Goniasteroidocrmu^ iuberosus — Lyon and Casseday; Amer. Jouni, Sci., Vol. XXA^III., (Ser. 2), 



, 233. 

 1866. Gilbertsocrinus (^Goniasieroidocr.) tuherosics — Meek and Worthen ; Geo). Re. Illinois, Vol. II., . 



220, with diagrams. 

 1881. Ollacrinus tuberosus — W. and Sp. ; Revision Palaeocr., Pt. II., . 219. 

 1889. Goniasferoidocrinus tuberosus — S. A. Miller; N. A. Geol. and Palseont., . 250; and 1891, Adv. 



Sheets 17th Re. Geol. Surv. Indiana, .51, Plate 9, Pig. 11. 

 Syn. Trematocrinus robustus Hall; 1860, Sul. Geol. Re. Iowa, . ^1 . 



Calyx large, a little higher than wide. Dorsal cup subcylindrical, 

 slightly constricted at the arm regions, its base deeply excavated. Ventral 

 disk flat, with deep interradial depressions; the appendages pendent, long, 

 and frequently branching. Plates tumid, the radials drawn out into elon- 

 gate nodes or obtuse spines, directed downward. 



Infrabasals small, almost completely covered by the column; forming 

 the bottom part of the concavity, of which the basals constitute the sides, 

 and the radials with large interradial plates between them form the rim 

 of an inverted cone on which the remainder of the calyx rests. Radials 

 longer than wide, considerably larger than the costals. The interradial 

 plates large and covered with a sharp node. Costals hexagonal and hepta- 

 gonal. Distichals two in the calyx, smaller than the costals, and about as 

 wide as long. Arm openings of the same ray widely apart, separated by 

 two or three interdistichals. Arms pendent, slender, branching, and with 

 long pinnules ; there being six ultimate arms to each arm opening. Caly- 

 cine appendages in ten pairs, disposed interradially ; those of adjoining rays 

 in sutural contact to about 12 mm. from the calyx, when the pairs separate, 

 and the two tubes take a sharp outward turn, so that their tips meet with 

 those of adjacent pairs. Each tube is composed of three rows of plates 

 longitudinally arranged, two of them occupying the ventral, the third the 

 dorsal side, so that there are six rows for the distance to which they are 

 united. The tubes generally branch once or twice; they are long, and 

 taper gradually to their tips. Interbrachials arranged longitudinally in 

 three series of plates of nearly equal size ; the anal side not distinct. Vent- 

 ral disk low-hemispherical, almost flat, the plates highly convex, those form- 

 ing the interradial depressions somewhat smaller. Orals a little larger than 

 the other disk plates, and rather irregular in their arrangement. Anus 





