168 Cincinnati Society of Natural History. 
Body, usually, very large, and sometimes having a length of 4 inches, 
and diameter of 24 inches; the specimen showing the vault, and repre- 
sented by fig. la, has a length of 24 inches, greatest diameter, 1 6-10 
inches, which is at the tup of the first secondary radials, diameter at 
the constriction below the arm bases, 1 3-10 inches. It gradually ex-_ 
pands from a sub-acute base to the first secondary radials, rapidly 
contracts to the fourth secondary radials, and slightly expands to the 
top of the vault. This is the normal form, though nearly every 
specimen is more or less irregular, apparently from pressure, and the 
base is usually turned to one side. 
Basals.—Basal plates, three, equal, hexagonal, and a little wider 
than high. 
Primary radials.—Three of the first radials rest upon the wider sides 
of the basals, and two in the angles formed at the junction of the basals. 
Three of them are hexagonal, and two heptagonal, though in one 
specimen examined, three are heptagonal, the left anterior first radial 
being heptagonal instead of hexagonal. They are a little higher than 
wide. In the hexagonal plates, the upper side is the shorter and the 
lower next in length. The second radials are, usually, hexagonal, 
nearly as large as the first, always longer than wide, but differing in 
the proportional length and width in different specimens. The left 
anterior second radial, in the specimen illustrated by fig. 1, is heptag- 
onal, but this seems to be abnormal, as in all other specimens ex- 
amined it is hexagonal. The third radials are larger than the second, 
and usually about the size of the first, though they are sometimes, as 
shown by fig. 1, larger. The left anterior plate in fig. 1, is octagonal, 
but the same plate, in the specimen illustrated by fig. la, has nine 
sides, four azygous interradials abutting upon it, instead of three. 
In fifteen specimens examined, I have found four third radials with 
nine sides, and one with seven. 
Secondary radials.—The first secondary radial, in all the specimens 
examined, is heptagonal, and about two thirds as large as the third ra- 
dial, with the exception of the octagonal plate in the left antero-lateral 
series, in the specimen represented by fig. 1. The second plate is 
smaller and heptagonal, but it does not, as in other instances, in this 
genus, support tertiary radials. This plate is succeeded by a third and 
a fourth secondary radial which gradually diminish in size, The fourth 
plate is followed by two smaller plates, and these again by others be- 
longing to the brachial series. The constriction occurs at the top of 
the fourth secondary radial, and from this point upward, for about 
