110 ISOPODA. 



chief modes of distribution of the groups hitherto pro- 

 posed. 



Latreille, having separated the anomalous genera lone, 

 ApseudeSy 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. SpHyEROMiDES (Sph&roma, &c., Anthurd) ; 



4. IDOTEIDES (Idotea, Arcturus) ; 



5. ASELLOTA (Asellus, &c.) ; 



6. ONISCIDES (Liaia, 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, Limnoma, 

 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, SpJueroma and Ancinus 

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

 JEga, 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- 



