278 THE CEINOIDEA CAMEEATA OF NOETH AMEEICA. 



ticlial spaces. The plates marked by rounded ridges, one to each side of the 

 plates ; those upon the radials and fixed brachials much wider and more 

 prominent. The ridges tapering to the margins of the plates, so as to form 

 bead-like elevations along the rays, and a well defined star upon each inter- 

 brachial. 



Basals large, forming an elongate cup, which is deejDly grooved at the 

 interbasal sutures, and the sides of the plates are bordered by conspicuous 

 ridges, which are prolonged to the upper part of the radials. Eadials and 

 costals large, longer than wide ; the radials larger than the costals. Dis- 

 tichals two. Palmars free from the fourth plate. Arms twenty, simple, 

 long, slender, gradually tapering to their tips, and beyond the fourth or fifth 

 plate strictly biserial. The first pinnule is given off from the second pal- 

 mars, and all succeeding brachials are pinnule-bearing. Interbrachials : 1, 2, 

 2, 2, 2, etc.; the lower one considerably the larger. Interdistichals : 1, 1, 1 ; 

 interpalmars : 2 to 3. Anal interradius the widest, the lower plates some- 

 what larger than the corresponding plate of the four other sides. It con- 

 tains three plates in the second and all succeeding rows, the middle series 

 marked by a somewhat interrupted longitudinal ridge. Similar but shorter 

 ridges proceed from the first anal plate to adjacent radials. Construction of 

 ventral disk, and position of anus not known. Column slightly decreasing 

 in size downward ; round ; composed of rather long joints with convex 

 edges ; the nodal joints considerably thickest. At three inches from the 

 calyx, each internode contains seven to eight joints, of which every second 

 or third is nearly as large as the nodal ones. 



Horizon and Locality. — Trenton limestone, Ottawa, Canada. 



Tf/pes in the Canada Survey Museum at Ottawa ; collected by Mr. John 

 Stewart. 



We take pleasure in dedicating this elegant species, the type of a new 

 genus, to our friend Mr. Walter R. Billings, the author of several important 

 papers on Crinoids, to whom we are indebted for many favors. 



PeriglyptOCrinus prisons (Billings), 

 Plate XXI. Fig. 2, 



1856. Glyptocrims prisons — E. Billings; Geol. Surv. Canada (Rep. of Progress), p. 287; also 1859, De- 

 cade IV. p. 56, Plate 7, Pigs. \a, b, c. 

 1881. Ghjptocrinus priscus ^y^ . and Sp. ; Revision Palaeocr., Part II., p. 189. 

 1883. Qlyptocrinus prisons — S. A. Miller; Journ. Cincin. Soc. Nat. Hist., p. 325. 

 1883. (?) AroJi(£oorimis prisons — y^ . and Sp. ; Revision Palseocr., Part III., p. 301. 



