ORDER L 

 CHORISTOPODA, OR TETRADECAPODA. 



The three divisions of the Choristopoda, the Amphipoda, Anisopoda, 

 and Isopoda, are pointed out on pages 10 and 11 of this Report, and 

 the reasons are there stated for rejecting the subdivision of Lcerriipoda, 

 introduced by Latreille. 



The Amphipoda are uniformly characterized by having — 



1. The three posterior pairs of thoracic legs in one series, and the 

 four anterior pairs in two other series of two pairs each. The branchiae 

 are thoracic. 



2. The abdominal members in two sets, the three anterior pairs 

 subnatatory, the three posterior styliform. 



The Isopoda through all the typical groups have 



1. The four posterior pairs of thoracic legs in one series, and the 

 three anterior in another series. The branchiae are abdominal. 



2. The abdominal members in two sets, the five anterior pairs 

 branchial (the first or exterior sometimes an operculum), the sixth 

 pair more or less styliform. 



Expressing these distinctions in figures, and numbering the pairs of 

 appendages 1 to 7 for the thorax, and 1 to 6 for the abdomen, we have 

 for the series in the 



Thorax. Abdomen. 



Amphipoda, .... 4 (or 2+2) : 3 3:3. 

 Isopoda, . . . . 3 (or 1+2) : 4 5:1. 



