THE FIRST ORDER OF ENTOMOSTRACA, 

 OR SIXTH OF THE CLASS OF CRUSTACEA. 



THE BRANCHIOPODA. 



The characters of this order are, a mouth composed of a 

 labrum, of two mandibles, of a ligula, and of one or two pairs 

 of jaws; gills — or the first of these organs, when there are se- 

 veral — always anterior. 



These Crustacea are invariably eiTatic, generally covered 

 by a testa in the form of a shield, or of a bivalve shell, and 

 provided with four or two antennse. Their feet, with some 

 few exceptions, are solely adapted for swimming. The num- 

 ber of their feet varies ; in some it is only six, in others, from 

 twenty to forty -two, or even more than a hundred. Many of 

 these animals have but a single eye. 



The majority of these Crustacea, being, as w^e have already 

 observed, almost microscopical, it is obvious that the applica- 

 tion of one of the characters which we have hitherto em- 

 ployed, namely the presence or absence of mandibulary palpi, 

 would, under such circumstances, present difficulties almost 

 insurmountable. We shall, however, place at the head of the 

 entomostraca, all the branchiopoda whose mandibles are pro- 

 vided with palpi. They will compose the first two divisions 

 of the lophyropa ; but the form and the number of the feet, 

 number of the eyes, and the testa, will furnish us with charac- 

 ters more easily to be employed, and more within the reach " 

 of general observation. 



The order of the branchiopoda in the methods of Degeer, 



