NIAGARA GROUP. 
187 
Genus GLYPTASTER (nov. gen.). 
[ Gr. yXutfro£, sculptilis, and aoVsp, Stella.] 
Pelvic plates five, marked by strong diverging ridges which unite on the plates of the 
second series, forming five strong ridges, which again bifurcate, sending one division to 
the base of each arm. Structure of upper part of cup unknown; arms ten, composed of 
a double series of plates. 
This species is closely allied to Glyptocrinus in the structure of the calyx, which can 
not be fully determined. 
581. 1. GLYPTASTER BRACHIATUS («. sp.). 
Pl. XLI. Pig. 4 a, fr. 
Structure of the calyx not ascertained ; surface granulate or tuberculated, in addition 
to the strong ridges ; arms ten, nearly cylindrical and much elongated. 
The specimen figured is the only one which has fallen under observation, and the 
shaly matter adheres so strongly to the plates as to render it impossible to ascertain the 
true structure. The arms are spread out on the surface of the stone, and the base of the 
specimen turned upward so that the junction of the arms with the plates below can not 
be seen. 
Fig. 4 a. The specimen as it appears on the surface of a slab of shale. 
Fig. 4 b. A part of one of the arms enlarged, showing more distinctly the arrangement of the plates 
of the arms. 
Position and locality. In the shale at Lockport. 
In the Lower Silurian period, there is a single species in the Chazy limestone, marked 
by strong ridges diverging from the centre to the margins of the plate; and another in 
the Hudson-river group, and the Blue limestone of the same age at the west. There is 
probably a third species, and possibly a fourth, in the Clinton group ; judging from the 
fragments of arms and columns found in that position, and figured on Plate A 41. These 
three, with the one figured above, are the only ones presenting these external characters 
at present known to me in the whole range of the New-York strata. Were it not that 
similar characters are shown (according to figures) in species of Actinocrinus from the 
Carboniferous period, I should be inclined to regard this marking as characteristic of 
Silurian crinoids. 
If' 
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