The crawfishes

have five feet on either side, including the
claws at the end; and in like manner the crabs have ten feet in all,
including the claws. Of the carids, the hunch-backed, or prawns,
have five feet on either side, which are sharp-pointed-those towards
the head; and five others on either side in the region of the belly,
with their extremities flat; they are devoid of flaps on the under
side such as the crawfish has, but on the back they resemble the
crawfish. (See diagram.)It is very different with the crangon, or
squilla; it has four front legs on either side, then three thin ones
close behind on either side, and the rest of the body is for the most
part devoid of feet. (See diagram.) Of all these animals the feet
bend out obliquely, as is the case with insects; and the claws, where
claws are found, turn inwards. The crawfish has a tail, and five fins
on it; and the round-backed carid has a tail and four fins; the
squilla also has fins at the tail on either side. In the case of both
the hump-backed carid and the squilla the middle art of the tail is
spinous: only that in the squilla the part is flattened and in the
carid it is sharp-pointed. Of all animals of this genus the crab is
the only one devoid of a rump; and, while the body of the carid and
the crawfish is elongated, that of the crab is rotund.