Giyptocrinus Redefined and Restricted, etc. 225 
¢ 
it bears forty arms. The radial ridges are moderately prominent. 
The interradial and intersecondary radial areas are slightly concave, 
- and filled with medium sized smooth plates. The column is round, and 
distinguished by its thin, sharp-edged plates near the head, and the 
eradual separation below o: the projecting plates until they are from 
one to three lines apart. This is a well ma:ked species in the struc- 
ture of the column, the arms, and in other respects. 
It occurs in the Trenton Group. 
;LYPTOCRINUS PRiscuS (Billings). 
G. priscus, has a pentagonal, obconoidal calyx, with smooth plates. 
There are five basals of moderate size, and three by five primary ra- 
dials, the first of which are very large. The number of secondary 
radials is not mentioned by Billings, but looking at his illustration one 
would infer there are fuur or more in each series. The radial ridges 
are prominent, and tke interradial areas depressed. A longitudinal 
row of larger plates fill the central part of the azygous area, and bear 
a strong ridge that bifurcates on the first azygous plate, and sends one 
branch to each of the contiguous first primary radials. The column is 
round, with the larger plates rather thick, nodulose, and somewhat 
distant from each other. There are only ten arms composed of short 
plates, and bearing moderately long pinnules. This is a strongly 
characterized species. 
It occurs in the Trenton Group. . 
GLYPTOCRINUS ORNATUS (Billings). 
G. ornatus has a broad oval calyx, well rounded at the base. Each 
of the plates is ornamented with five or six sharp ridges, which radiate 
from the center, thus covering the body with numerous stars, with tri- 
angular spaces. There are five basals, three by five primary radials, 
and as near as I can ascertain from the specimens in my own collec- 
tion, five by ten secondary radials. Billings does not mention the 
number of these plates. The interradial and intersecondary radial 
areas are slightly concave, and the plates are rather large, and not 
more numerous than they are in G. decadactylus. There are only ten’ 
arms. The column is round, and the larger plates thin and sharp- 
edged, and gradually become more distant from each other as they re- 
cede from the calyx. This is a beautiful, well marked species. 
It occurs in the Trenton Group. 
