SYSTEMATIC 

 ARRANGEMENT OF CRUSTACEA, 



CLASS X. 

 CRUSTACEA. 



ARTICULATE animals apterous, supplied with articulate feet 

 both thoracic and abdominal, breathing mostly by branchiae, some- 

 times by the skin, without stigmata. Heart very often distinct, 

 aortic, situated in the back. 



Sexes in most distinct. Animals mostly aquatic. 



ORDER I. Pmcilopoda. 



Jaws none. Feet of cephalothorax placed round the mouth, 

 with coxae very spinose, performing the office of jaws. Abdominal 

 feet resembling semi-orbicular lamellae, bearing the branchiae. Two 

 shields, gibbous above, hollowed beneath, horny, hard, one covering 

 the cephalothorax, the other the abdomen. 



Family I. Xiphosura. (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. 



Limulus MUELL. (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 



