212 
CLASS CRUSTACEA. 
Typhis, Risso, 
Have but two very small antennae. The head is thick, and 
the eyes not projecting. Each pair of feet is annexed to a 
proper segment : the anterior four are terminated by a didac- 
tylous pincer. On each side of the thorax are two mobile 
laminae, forming sorts of shutters, or valves, which, united, 
when the animal folds its feet and tail underneath, close the 
body interiorly, and give it the form of a spheroid. The pos- 
terior extremity of the tail is without appendages. {Typhis 
oroides, Risso.) 
AnceIjs, Risso, Gnatliia, Leach, 
Which have also the thorax divided into as many segments, 
as pairs of feet, but in which all those organs are simple and 
monodactylous. They have, besides, four antennae (setace- 
ous.) The head is strong, squared, with two large projections 
in the form of mandibles. The extremity of the tail has some 
foliaceous appendages in the form of fins. {Anceus for/icula- 
ris, Risso.) 
Praniza, Leach, 
■v 
Have four setaceous antennae, as well as Anceus ; but the 
thorax seen above presents only three segments, the first two 
of which, very short and transverse, have each one pair of 
feet, and the third, much larger and longitudinal, bear the 
others. All the feet are simple. The head is triangular, 
pointed in front, with the eyes projecting. The posterior ex- 
tremity of the body also presents a fin on each side. {Oris- 
ons cceruleatus , Montagu.) 
