930 DIVISION Il MOLLUSCOUS ANIMALS.—CLASS III. GASTEROPODS. 
the back, and upon the head a very large membranous fringed veil, which 
curves in its contraction under the mouth. 7. fimbria is a beautiful Med- 
iterranean species, of a grayish color, spotted with white. The remaining 
genera are SCYLLEA, Guaucus, Eourp1a, and TERGIPEs. 
Nothing can be more elegant or various than the form and arrangement 
of the gills in most of the Nudibranchiates. In the Glawet and Scylla 
we see at each side of the elongated body long arms, branching out into 
tufted filaments, and on the back of /Holides the gills are arranged in rows, 
while in the Vorides they form a regular wreath, or garland, round the 
lower intestinal aperture. The beauty of these animals corresponds with 
their mythological names; for every part of them which is not sparkling 
like the purest crystal, shines with the liveliest colors. Some of them creep 
along the coast; others seek the open sea, where they attach themselves to 
floating alew, or swim about upon their back, by rapidly contracting the 
border of their mantle. 
Although they are represented in all seas, they delight particularly in the 
warmer latitudes. Though provided with no defensive weapons, they are 
not left altogether to the mercy of their enemies. Some conceal themselves 
under stones; and some, on contracting, cast off parts of their mantle, 
leaving it in possession of their hungry foe, while they themselves make 
their escape. 
ORDER III. INFEROBRANCHIATA. 
The Inferobranchiates resemble the Dorides and Tritones in their habit 
and organization ; but their branchiw, instead of being situated upon the 
back, are on the sides of the body, under the projecting margin of the 
cloak, where they form two long series of leaflets. They are incapable of 
swimming. The genera are Puytiipta and Dipnyiipes. The former 
group belongs to the Indian Ocean; the latter lives in stagnant waters, and 
in rivulets, adhering to stones and aquatic plants. 
ORDER IV. TECTIBRANCHIATA. 
In this order the branchiw are attached along the right side, or upon the 
back, in the form of leaflets, more or less divided, are more or less cov- 
ered by the mantle, which generally contains a small shell. This order 
comprehends several groups, of which the most remarkable is the genus 
Apnysta. — The mantle of this animal forms two wide folds on the back. 
When these are opened, the delicately-fringed branchiz appear in a deep 
