62 
NATURAL HISTORY. 
[N. ZOOL. GAL. 
cording to the structure of the hard particles which form 
the support of the body, and which generally agree with 
the external form of the body. 
The Astropectens (Cases 13 and 14,) have the back of the 
rays thin and netted, with numerous tubercles at the junc¬ 
tion of each of the little bones, which are covered at their 
tips with numerous small moveable spines. They are the 
most beautiful of the order. 
The Pentaceridcz (Cases 15 to 17,) have the skeleton 
formed of large roundish tubercles, the skin between 
which is pierced with small holes ; some of these have a 
convex back and triangular arms, as the Pentaceros; 
others are flat above and beneath, with five broad, short 
rays edged with larger pieces, as Goniaster; many of 
these have their back studded with conical tubercles, 
which enlarge in size as the bone on which they are placed 
increases ; these tubercles sometimes fall off as the animal 
increases in size, and are easily separated, leaving a flat 
scar when the specimen is dead. Some of them, as the 
Dactylosaster , Case \1, have elongated cylindrical arms. 
The last family, or the Asterinidce , have the skeleton 
formed of compressed pieces, placed one over the other 
like the tiles on a house ; they always have a thin mar¬ 
gin. They are generally flat and pentangular, but some 
have a convex back, and a few are many rayed. (Case 18.) 
The Lizard-tailed Stareishes, Ophiurida, (Cases 
19 to 24,) have a suborbicular depressed body with five 
cylindrical, jointed, very flexible arms, which are some¬ 
times repeatedly divided into branches ; the arms are 
furnished with a series of small pores, along each side of 
their under or oral surface, and they have a lunate hole on 
each side of the base of their arms. They have no dorsal 
warts. 
The family Ophiuridce have an orbicular body covered 
with spines or scales, and the arms, which are always 
simple, are furnished with cross series of spines on the sides. 
In some, ( Ophiosoma , Cases 19,20,) the spines of the arms 
are long and expanded, in others, as Ophiura , they are short 
and appressed. Most of the species have five rays, there is 
one in the collection (Case 20) with only four, and some 
have been described as having eight, but they are only 
monstrosities. 
