CRUSTACEA. 307 



with small spines round a large central pharynx. At others they 

 either compose a little siphon or beak, used for suction, as in seve- 

 ral 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 PJECILOPODA. 



FIRST GENERAL DIVISION. 

 MALACOSTRACA. 



The Malacostraca naturally divide themselves into those whose 

 eyes are placed on a movable pedicle, and those in which they are 

 sessile and fixed. 



a. Eyes placed on a movable and articulated pedicle. 



ORDER I. 



DEC APOD A(l). 



The head, in the Decapoda, is closely joined to the thorax, and 

 covered with it by a shell, entirely continuous, but that most fre- 

 quently exhibits deep lines dividing it into various regions which in- 

 dicate 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 easily digested. The body of some Palinuri attains 

 the length of a metre. Their claws are efficacious weapons, and 



(1) Ten-Footed. 





