114 1SOPODA. 



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 

 Liriopinge are more properly referable to the Bopyridse. 

 4thly, the Crossurinse are synonymous with Tanais, the 

 genus Crossurus (Rathke), on which Dana has founded the 

 subfamily, being a true Tanais. And 5thly, the Bopyrinse 

 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 Hyperiidse 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. 



* Aim. Sei. Nat. torn. iv. p. 323, 1365. 



