362 PROCEEDINGS OF THE ACADEMY OF [1881. 



radial, long, slender, simple from the second division, rounded on 

 the outer side, and composed of a single series of short, some- 

 what wedge-shaped pieces, of which each one supports at its 

 larger end a pinnule. Pinnules very slender, alternately and very 

 closely arranged, the proximal ones fixed in the body walls, the 

 first generally given off from the second secondary radials. 



Interradial arese occupied by a large number of pieces, 

 arranged in four or more series, with one plate in the first, two in 

 the second, and generally three in each succeeding series. The 

 posterior or anal area differs from the others in being a trifle 

 wider, and having three plates instead of two in the second and 

 all succeeding series. The median row generally consists of 

 larger plates, and these elevated above the level of the others. 

 The first anal, like the first interradial plate, rests upon the upper 

 sloping side of the first and between the second radials. Inter- 

 axillary plates from one to ten, with a less number in species in 

 which the last bifurcation takes place in the body. 



Vault scarcely elevated above the horizon of the arm bases ; the 

 interradial regions somewhat depressed ; composed of numerous 

 very small, convex plates. The apical dome plates not well 

 defined ; anal aperture directlj- through the vault, excentrie. 



Column round, of medium size ; central canal small, distinctly 

 pentagonal. 



Geological Position, etc. — Glyptocrinus, as amended by us^ 

 occurs exclusively in the Lower Silurian at the age of the Trenton 

 and Hudson River groups, and apparently only in America. 



We recognize the following species : — 



1879. Glyptocrintis angularis Miller and Dyer. Jour. Cincin. Soc. Nat. Hist., p. 5, 

 PI. 1, fig. 10. Hudson River gr. Cincinnati, Ohio. 



1847. Glyptocr. decadactylus Hall. Type of the genus. Paleont. N. York, i, p. 

 281, PI. 77, figs. 1 a^f, and PI. 78, figs. 1 a-u; also Geol. Rep. Ohio, 

 Paleont., i, p. 30, PI. 2, figs. 5 a, b; Zittel, Handb. der Palaeont., i, p. 375, 

 figs. 262. Hudson River gr. Cincinnati, Ohio. 



1872. Glyptocr. Dyeri Meek. Proe. Acad. Nat. Sci. Phila., p. 314 ; also Geol. Rep. 

 Ohio, Paleont., i, p. 32, PI. 2, figs. 2 a, b (not 2 c). Hudson River gr. Cin- 

 cinnati, 0. 



1855 (?) Glyptocr. fimbriatus Shumard. Geol. Rep. Missouri, by Swallow, pt. ii, p. 

 194, PI. A, figs. 10 a, b. Trenton gr. Cape Girardeau, Mo. 

 This species evidently does not belong to Glyptocrinus, description and figure 

 are too imperfect to place it correctly. 



1874. Glyptocr. Fornshelli S. A. Miller. Cincin. Quart. Journ. Sci. Hudson River 

 gr. Cincinnati, Ohio. 



