58 THE LIFE OF CRUSTACEA 



instead of being freely exposed. While agreeing in 

 these essential characters, however, the members of 

 the order Decapoda differ very widely among them- 

 selves in structure and in general form, and they are 

 classified (in the arrangement adopted here) in two 

 suborders, which are again subdivided into sections 

 and tribes. 



Order DECAPODA. 



rTribe Penaeidea. 

 Suborder Natantia - \ „ Stenopidea. 



Caridea. 



Reptantia. 



Section Pa/mura {_j;_|ryonidta!' 



,, Astaciira - ,, iS^ephropsidea. 



c ,, Galatheidea. 



Ano7mira 



_ J ,, Thalassinidea. 

 ' \ ,, Paguridea. 

 I ,, Hippidea. 

 r ,, Dromiacea. 

 „ Brachyura - J ,, Oxystomata. 



\ ,, Brachygnatha. 



Subtribe Brachyrhyncha. 

 ,, Oxyrhyncha. 



The suborder Natantia includes the numerous 

 species of what are commonly known as Prawns 

 and Shrimps. These are characteristically powerful 

 swimmers, with lightly armoured bodies, more or 

 less flattened from side to side, with a thin, saw- 

 edged rostrum, and with large swimmerets which are 

 the chief organs of swimming ; in addition, some of 

 the more primitive Natantia have swimming branches, 

 or exopodites, like those of the Euphausiacea, on the 

 thoracic legs. This suborder is divided into three 



