EHODOCRINID^. 247 



Horizon and Localihj. — Lower Burlington limestone ; Burlington, Iowa. 



Type in the Museum of Comparative Zoology, Cambridge. 



Remarks. — This species is distinguished from G. tyims 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 (Hall). 



Plate XT. Figs. 8a, h, c. 



1862. Trematocrimis spinigerus — Hall; ISth Hep. N. Y. State Cab. Nat. Hist., p. 128. 



1866. Goniasteroidocrinus spinigerus — Meek and Worth. ; Geol. Surv. Illinois, Vol. XL, p. 222. 



1872. Gilbertsocrinus {Trematocrinus) spinigerus — Hall; New York State Mus. Nat. Hist., Bull. I., Plate 



la, rig. 9 (privately distributed). 



1877. Goniasteroidocrinus spinigerus — S. A. Miller; Cat. Amer. Palseoz. Poss., p. 80. 



1881. Ollacrinus spinigerus — W. and Sp. ; Revision Palseocr., Part II., p. 219. 



1889. Goniasteroidocrimts spinigerus — S. A. Miller ; North Amer. Geol. and Paleeont., 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 decagonal 

 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. Eadials 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. 

 Calycine 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, 3, 3, and 

 two plates. Interdistichals three or more. Yentral disk flat, with deep 



