134 
NATURAL HISTORY. [NEW BUILDING. 
The family of Spatangidce (Cases 9, 10 ,) differ from all 
the others in the mouth being transverse, and more or 
less in front of the middle of the under side of the shell. 
They are destitute of jaws 5 the series of pores are ge¬ 
nerally interrupted, but they form petal-like rows, both 
on the back and near the mouth. The shell is generally 
heart-shaped, with a groove from the crown to the mouth 
in front, and they are sometimes furnished with long 
slender as well as the usual small short spines. The 
cases or shells of these animals are formed of the same 
number of bands as the other Sea Eggs, but the bands are 
of unequal breadth, as is sometimes the case with deformed 
specimens of the hemispherical Echini. (See specimen in 
Case 2 .) 
The Holothurida or Sea Cucumbers have many 
characters in common with the Echhiidce , but their skin is 
only hardened with irregular scale-like or oblong bones; 
their mouth is in general surrounded with 5 or 10 plu¬ 
mose appendages. Most of them are furnished with 
rows of pores similar to, and for the same purpose as, 
the ambulacra of the Echinidee ; in some, as the Holo - 
thuria , they form regular lines from the mouth to the 
vent ; in others, as the Cuvieria , (Case 10,) they are all 
crowded on the under surface of the body, which is in 
general flat. 
The family of Siphunculidce have many characters in 
common with those animals, but they are destitute of any 
ambulacra. 
The Holothuridce and Siphunculidce are eaten; the 
Trepang , a common name of the various species of 
the former genus, is much sought after by the Chinese to 
flavour their soup. Also see the specimens of this order 
in Room VII. 
The Hypostomata, (Cases 11 to 24,) differ from the 
former class in the body being expanded into rays or 
lobed, and in having a bag-like stomach, with only a 
single aperture through which the food is received, and 
the indigestible part rejected. It contains the Asteroida 
and Ophiurida . 
The true Star-Fishes, or Asteroida, (Cases 11 to 18,) 
have the body expanded into arms of the same structure 
as itself, and the under sides of the arms are marked with 
