136 
NATURAL HISTORY. [NEW BUILDING. 
gin. They are generally fiat and pentangular, but some 
have a convex back, and a few are many rayed. (Case 18.) 
The Lizard-tailed Starfishes, Ophiurida, (Cases 
19 to 24,) have a suborbieular 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 Ophiurid<je 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 th£ collection (Case 20) with only four, and some 
have been described as having eight, but they are only 
monstrosities. 
The family of Gorgon heads, ( Euryalidce ,) on the con trarv, 
have the body covered with a leathery skin and strength¬ 
ened behind with five pairs of radiating ribs. The arms 
are compressed and furnished with a series of pores on each 
side ; the outer side of each pore is partly covered with a 
bundle of small spines arising from a common base. 
The arms of the Astrophyton (Cases 22 and 23) are 
round and repeatedly branched so as to end in very small 
flexible filaments, by which the animal attaches itself to 
marine bodies and strains its food from the surrounding 
water. The Enryale has square arms only branched at 
the tip. The Natalia has round simple tubercular ringed 
arms. The Laspalia only differs from the former in 
having elongated simple arms covered with a crustaceous 
coat. 
The remainder of the Echixodermata have a purse-like 
body, and the middle of their back is produced into an 
elongated stem, by.which they are often attached to other 
bodies, or if they are free, the middle of their back is fur¬ 
nished with a bunch of hooked fibres, by which they attach 
themselves to corals, sea-weeds, &c.; and some of those 
which are free in their adult state are attached by a pedun¬ 
cle when very young. 
