110 ISOPODA. 
chief modes of distribution of the groups hitherto pro- 
posed. 
Latreille, having separated the anomalous genera Jone, 
Apseudes, Anceus, and Praniza (which he placed among the 
Amphipoda), divided the remainder of the order into six 
sections :— 
1. Eprcarrpes (Genus, Bopyrus) ; 
2, CymotHoapa (Serolis, Cymothoa, &c.) ; 
3. SpomromivEs (Spheroma, &e., Anthura) ; 
4. Iporrrpes (Idotea, Arcturus) ; 
5. AseLLora (Asellus, &c.) ; 
6. OniscipEs (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. Isopoprs 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. IsopopES 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, Spheroma and Ancinus 
(allied to Serolis 2). 3. Cymothoadiens (Genera, Serolis, 
Alga, Cirolana, and Cymothoa, &c.). 
3. IsoOPODES SEDENTAIRES, with the mouth more or 
less rudimentary (Genera, Bopyrus and Jone). 
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- 
