NATURAL HISTORY. 
117 
ROOM II.] 
The family of Typical Star-Fishes (Asteriadje, Cases 11 and 12) 
have four series of holes and tentacles in each of the arm-grooves. 
Most of the kinds have only two series of pores in each groove ; they 
are divided into groups of genera, according 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 family of Astropectenhle (Cases 13 and 14) have the back of 
the rays thin and netted, with numerous tubercles at the junction 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 family of Pentaceridh: (Cases 15—17) have the skeleton 
formed of large roundish tubercles, the skin between winch 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, wilich enlarge in size as 
the bone on winch they are placed increases; these tubercles some¬ 
times fall off as the animal increases in size, and are easily separated, 
leaving a fiat scar w T hen the specimen is dead. Some of them, as the 
Dactylosaster, (Case 17,) have elongated cylindrical arms. 
The last family, or the Asterinid^e, have the skeleton formed of com¬ 
pressed pieces, placed one over the other like the tiles on a house; they 
always have a thin margin. 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—24,) 
have a suborbicular depressed body with five cylindrical, jointed, very 
flexible arms, w T hich are sometimes 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 of Ophiurhle 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. 
The family of Gorgon heads, (Euryalid^e,) on the contrary, have 
the body covered with a leathery skin and strengthened 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 re¬ 
peatedly 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 Euryale 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 Echinodermata 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 
