116 ISOPODA. 
Group—ABERRANTIA. 
Tu1s group is formed of those crustacea which, al- 
though belonging in certain important conditions to the 
order Isopoda, offer peculiar aberrant characters. 
In the Amphipoda the branchial organs are (as in 
the Podophthalmic orders) attached to the appendages 
of the body. In the aquatic Isopoda they are attached 
to the fourth and fifth pairs of the appendages of the _ 
tail. But in the several genera which we link together 
to form this group, the branchial organs have not been 
made out; indeed, both Dr. Fritz Miller and Prof. 
Lilljeborg assert that no such organs exist. 
In one genus alone (and possibly only in certain 
individuals of that genus) we have detected a saccular 
appendage attached to the coxa of the third pair of 
pereiopoda (or fifth pair of legs), that can, we think, 
only be interpreted as a branchial organ similar to those 
which exist in the Amphipoda attached to most of the 
legs. Again, in Amphipoda, the heart lies beneath the 
dorsal surface of the body, in the Isopoda in the tail. 
In Tanais and Apseudes, according to Dr. Fritz Miller, 
the heart is situated as in the Amphipoda. And in the 
embryonic condition the development is after the manner 
of the Amphipoda rather than that of the Isopoda. 
We restrict this group to the typical genera of Dana’s 
sub-order Anisopoda. It also corresponds with Dr. 
Milne Edwards’ AssELOTES HETEROPODES, to which we 
have added the family of ANTHURID&. 
This group, in consequence of the variation in habits, 
we have divided into two tribes, VaGanTia and Sus- 
PARASITICA. 
ee UL 
