110 } ISOPODA. 



chief modes of distribution of the groups hitherto pro- 

 posed. 



Latreille, having separated the anomalous genera lone, 

 ApseudeS) Anceus, and Praniza (which he placed among the 

 Amphipoda), divided the remainder of the order into six 

 sections : 



1. EPICARIDES (Genus, Bopyrus)\ 



2. CYMOTHOADA (Serolis, Cymothoa, &c.) ; 



3. SPIOEROMIDES (Spharoma, &c., Anthurd) ; 



4. IDOTEIDES (Idotea, Arcturus) ; 



5. ASELLOTA (Asellus, &c.) ; 



6. ONISCIDES (Ligia, Oniscus, &c.) ; 



thus commencing with the abnormal parasitic species, and 

 terminating with the terrestrial ones. 



Professor Milne Edwards adopted a different principle 

 of classification, dividing the order into three sections : 



1. ISOPODES MARCHEURS, in which the terminal ap- 

 pendages of the tail are styliform or opercular, and never 

 formed into swimming appendages, consisting of three 

 families Idoteides (Genera, Arcturus, Idotea, and An- 

 thura). 2. Asellotes (Genera, Apseudes, Tanais, Limnoria, 

 Asellus, &c.). 3. Cloportes (Genera, Ligia, Oniscus, &c). 



2. ISOPODES NAGEURS, in which the terminal appen- 

 dages of the tail form a swimming apparatus, consisting 

 of three families: 1. Praniziens (Genera, Praniza and 

 Anceus). 2. Sphaeromiens (Genera, Spharoma and Ancinus 

 (allied to Serolis ?). 3. Cymothoadiens (Genera, Serolis, 

 Mga^ Cirolana, and Cymothoa, &c.). 



3. ISOPODES SEDENTAIRES, with the mouth more or 

 less rudimentary (Genera, Bopyrus and lone). 



Here we find the four anomalous genera placed by 

 Latreille among the Amphipoda referred to the present 

 order, and Latreille's general arrangement nearly re- 



