THE CLASSIFICATION OF CRUSTACEA 45 



feet are all alike, and are flattened and leaf-like in 

 form, resembling those of the Branchiopoda. The 

 first four pairs of abdominal limbs are large two- 

 branched swimming feet, but the last two pairs are 

 reduced to small vestiges. Two of the most impor- 

 tant points in which the Nebaliacea differ from all 

 the other Malacostraca are that there are seven 

 instead of six somites in the abdomen (the last 

 somite has no appendages), and that the telson has 

 connected with it a pair of movable rods forming a 

 " caudal fork " like that of the Branchiopoda. On 

 account of the leaf-like thoracic feet and the posses- 

 sion of a caudal fork and other features, the Nebaliacea 

 were formerly classified with the Branchiopoda, 

 but a closer examination of their structure has 

 shown that they are true Malacostraca. In having 

 an additional somite in the abdomen and in other 

 points, however, they may be regarded as forming a 

 link between the Malacostraca and the lower forms 

 of Crustacea, and for this reason they are set apart 

 as a series LEPTOSTRACA, while the other orders 

 form a series EUMALACOSTRACA. 



The orders of the Eumalacostraca, again, are 

 grouped, as shown in the table of classification, into 

 four divisions. The first of these, the SYNCARIDA, 

 includes only one order, comprising a few small 

 Crustacea (see Fig. 84, p. 264) which have recently 

 been discovered in fresh water in Tasmania and 

 Australia. They have no carapace, and all the 



