New Species of Fossils and Remarks upon Others. 171 
as large as the second radials; this is succeeded by about five pairs, be- 
fore reaching the interbrachial spaces, though there is a third plate in- 
__ tervening, at about the height of the first secondary radials. Inter- 
secondary radials, five. The first is hexagonal, and as large as the 
second secondary radials. It is succeeded by two pairs of smaller 
_ plates. 
Azygous interradials.—The azygous area contains thirty-two plates, 
and has somewhat the appearance of two regular interradial areas, 
separated by a single series of plates. The first azygous interradial 
is heptagonal, rests between the sloping sides of the basals, and 
is like the heptagonal first radials. From the upper side, a series of 
seven plates extend as high as the arm bases, and are succeeded by 
smaller plates which cover the elevated rounded ridge which passes 
up over the convex vault and terminates with a small proboscis at 
the center. Between the upper sloping sides of the first azygous in- 
terradial and the adjacent interradials, on either side, there is an hex- 
agonal plate, which is succeeded by five pairs, very much as in the reg- 
ular interradial areas, and also containing an intervening plate at 
about the height of the first secondary radials. 
Vault.—The vault is highly convex, with a small central proboscis 
and an elevated ridge extending down the middle of the azygous area. 
The elevations indicating the connection of the ambulacral furrows, 
show five rays, in the central part of the vault, which soon bifurcate, 
forming ten rays, and these again divide before reaching the margin of 
the vault, making twenty elevated ridges, which extend down the cup 
to the arm bases, and represent the ambulacral furrows. The spaces 
between the ambulacral ridges are concave depressions more deeply 
excavated as they approach the margin of the vault. There are a few 
-_ interbrachial plates, but they so graduate upward in these concave de- 
pressions, to the plates of the vault, that from our specimens they are 
not accurately determinable. The vault is covered by numerous poly- 
gonal plates, the larger ones occurring in the concave depressions. 
Arms.—Arms twenty, and from the evidences they were composed 
of a double series of plates. 
This species is distinguished trom S. marcouanus, by its short, urn- 
shaped cup, and by the concave depressions in the vault, as well as by 
the presence of tertiary radials, twenty arms, and a less number ot 
plates. It is distinguished from S. christyi, by its shorter cup, the 
concave depressions in the vault, the presence of interbrachials, the 
less number of plates below the brachials, and by various other 
