112 ISOPODA. 
~ 
Amphipoda, which form the subject of our former 
volume, and the Isopoda, in which the tail is short, with 
the articulations admitting of little flexion, and with 
four or five pairs of abdominal appendages, which are 
lamellar and branchial, and only the posterior styliform. 
The Isopoda, moreover, are further distinguished by 
having only the three anterior pairs of thoracic feet di- 
rected forwards (instead of four, as in the Amphipoda), 
and four pairs directed backwards. 
These two primary groups he, moreover, considers to 
be united together by such genera as Tanais, Arcturus, 
&e., which he affirms agree with the Amphipoda, in 
having the four anterior pairs of legs directed forwards, 
and the three posterior pairs backwards; but, like the 
Isopods, they have the pleon very short, with only the 
last pair of members styliform, the others being lamellar 
and branchial, as in the Isopods. These, therefore, he 
proposes to form into a third tribe, to be called Aniso- 
poda, 
As the most recent revision of the animals comprised 
in the present volume, it will be useful to give the follow- 
ing condensed sketch of his arrangement of the two tribes, 
Isopoda and Anisopoda. 
Tribe 1, Isopoda. 
Subtribe 1, Idotzeidea. 
Fam. 1, Idotaide. 
Fam. 2, Chetilide. 
Subtribe 2, Oniscoidea. 
Fam. 1, Armadillida.—Subfam. 1, Tyline; sub- 
fam. 2, Armadilline. 
Fam. 2, Oniscida.—Subfam. 1, Oniscine; sub- 
fam. 2, Seyphacine ; subfam. 3, Lygine. 
Fam. 3, Asellidee.—Subfam. 1, Limnorine ; sub- 
fam. 2, Aselline. 
