THE CLASSIFICATION OF CRUSTACEA 57 



the sea. In these the carapace fuses with all the 

 thoracic somites, the eyes are stalked, the antennules 

 have two flagella, and the antennae have a broad 

 scale. None of the thoracic limbs are modified into 

 maxillipedsj and all carry swimming exopodites. 

 The uropods and telson form a tail-fan. A single 

 series of feathery gills are attached to the bases of 

 the thoracic limbs. Nearly all the Euphausiacea 

 possess the power of emitting light, and are furnished 

 for the purpose with a number of organs which were 

 formerly supposed to be " accessory eyes." 



The second order of the Eucarida, the Decapoda, 

 is by far the largest of the orders of Crustacea, and 

 it includes all the larger and more familiar members 

 of the class. It is necessary, therefore, to give a 

 considerably fuller account of its subdivisions than 

 has been given in the case of the other orders. 

 The typical characters of the Decapoda are well 

 illustrated by the Lobster, which has been already 

 described. As in the Euphausiacea, the eyes are 

 stalked, and the carapace fuses with all the thoracic 

 somites. From the Euphausiacea the Decapoda 

 differ in the fact that three pairs of the thoracic 

 limbs are modified as maxillipeds, the remaining five 

 pairs forming the " ten legs " to which the name of 

 the order alludes. Further, the gills are arranged 

 in more than one series, not all attached to the 

 bases of the legs, as in the Euphausiacea, and 

 covered over by the side -flaps of the carapace 



