114 ISOPODA. 
so strong a relationship to Idotea, through its opercular 
breathing apparatus, that it ought not to be far removed 
from it. So, also, Anthura, although the structure of the 
breathing apparatus of the tail appendages is very pecu- 
liar, possesses in its elongated form and nearly uniform 
feet only a relation of analogy with Arcturus, its relation 
with Tanais having been hitherto mistaken. 3rdly, the 
Liriopine are more properly referable to the Bopyride. 
4thly, the Crossurine are synonymous with Tanais, the 
genus Crossurus (Rathke), on which Dana has founded the 
subfamily, being a true Tanais. And 5thly, the Bopyrine 
are strictly Isopods so far as the legs are concerned; 
the structure of the mouth, parasitic habits, and remark- 
ably degraded condition of the female sex, constituting 
them into a solitary group far removed from the other 
Isopods, and analogous to the Hyperiide among the 
Amphipoda. With these prefatory remarks we beg 
to propose the following tabular arrangement of the 
Order, in which we have availed ourselves of the most 
important peculiarities of each mode of classification 
alluded to above. We consider, on the one hand, that 
Tanais, by the presence of branchial vesicles attached to 
the body, approaches nearest to the Amphipoda, and, 
on the other hand, that Oniscus, from the presence 
of internal spiracles, as has been recently shown by 
Wagner,* comes nearest to the Insecta, and, conse- 
quently, these two genera form the extreme limits of the 
order, 
* Ann. Sci. Nat. tom. iv. p. 823, 1865. 
