292 CRUSTACEA. 



external ones are naked or are not covered by the foot-jaws, approxi- 

 mate to the preceding Crustacea. In the other Entomostraca, which 

 seem to approach the Arachnides in several particulars, the organs of 

 manducation are sometimes simply formed by the coxae of the feet, pro- 

 jecting and arranged like lobes bristling with small spines round a large 

 central pharynx. At others they either compose a little siphon or beak, 

 used for suction, as in several Arachnides and Insects, or they are 

 wholly (or nearly so) invisible externally, either because the siphon is 

 internal, or because the suction is produced in the manner of a cup. 



The Entomostraca are thus dentated or edentated. The first will 

 form our order of the BRANCHIOPODA, and the second that of the 

 PJECJLOPODA. 



FIRST GENERAL DIVISION. 

 MALACOSTRACA. 



THE Malacostraca naturally divide themselves into those whose eyes 

 are placed on a moveable pedicle, and those in which they are sessile and 

 fixed. 



a. EYES placed on a moveable and articulated pedicle. 



ORDER I. 



DECAPODA*. 



THK head, in the Decapoda, is closely joined to the thorax, and covered 



with it by a shell, entirely continuous, 

 but that most frequently exhibits deep 

 lines dividing it into various regions 

 which indicate the places occupied by 

 the principal internal organs. The mode 



of their circulation presents characters which distinguish them from the other 



Crustacea. 



These animals grow but slowly, and live a long time. It is among them 



that we find the largest and most useful species, but their flesh is not 



* Ten-footed. 



