SYSTEMATIC 
ARRANGEMENT OF CRUSTACEA. 
CLASS X. 
CRUSTACEA. 
ARTICULATE animals apterous, supplied with articulate feet 
both thoracic and abdominal, breathing mostly by branchiz, some- 
times by the skin, without stigmata. Heart very often distinct, 
aortic, situated in the back. 
Sexes in most distinct. Animals mostly aquatic. 
OrvER I. Peecilopoda. 
Jaws none. Feet of cephalothorax placed round the mouth, 
with coxe very spinose, performing the office of jaws. Abdominal 
feet resembling semi-orbicular lamelle, bearing the branchie. Two 
shields, gibbous above, hollowed beneath, horny, hard, one covering 
the cephalothorax, the other the abdomen. 
Family I. Xtphosura. (Characters of the order.) Twelve 
pairs of feet, six attached to the cephalothorax, six to the abdomen. 
An appendage elongate, acuminate, carinate or gibbous above, 
plane beneath, adhering by articulation to the posterior part of the 
abdominal shield, covered by very hard skin. 
Timulus MvuEwu. (Polyphemus LAm.). 
This genus contains only few species, and is the only one in this 
family. The anterior shield is round forwards, and terminates on 
each side behind in a point, which extends along the outside of the 
second shield, which is of less breadth, about as far as its middle. 
This second or abdominal shield has an irregular hexangular form, 
and is armed on each side with seven sharp teeth and six moveable 
