These have peculiar flat bodies, greatly compressed, but in a direction
different from the flat Fishes of the Ray family. In the case of the
Raia, the body is flattened horizontally, but in the Fishes belonging to
this family the bodies are compressed laterally—like that of the
well-known Flounder. The head of the Fishes of this group are not
symmetrical; the two eyes are placed on the same side, and the two sides
of the mouth are unequal. These strange flat Fishes are always turned
upon their side, and the side turned towards the bottom of the sea is
that which has no eye. It is to this habit of swimming on their side
that they owe their popular name of side-swimmers.
They advance through the water very slowly compared with the motion of
other Fishes. They can ascend or descend in the water very quickly, but
cannot turn to the right or left with the same ease as other Fishes.
This property of rapidly rising or sinking in the water is more useful
to them, as they spend the greater part of their time at the greatest
depths, where they draw themselves along the sands at the bottom of the
sea, and often hide themselves from their enemies.