362 ARCTURIDE. 
character of the three following pairs, are considerably 
shorter and broader, and being more closely applied to 
the mouth, they appear to represent a second pair of 
maxillipeds, so that the animals may almost be regarded 
as exhibiting the anomalous condition of having two 
pairs of foot jaws and six pairs of legs, instead of one 
pair of the former and seven of the latter, as in the 
ordinary Edriophthaima, or three pairs of the former and 
five of the latter, as in the Decapoda. 
It is in such anomalous groups as these that we see 
the advantage, in a scientific point of view, of the identi- 
fication of each part by a name that is homologically 
true, instead of varying the term with the variation of 
form or use that the necessities of animals require. If 
we adopted the latter plan, as is too frequently the case 
even among some of the best carcinologists, we should be 
obliged to name the four anterior pairs of legs in this 
genus as four pairs of maxillipeds, and which, added to 
the pair which is homologically consistent, would make 
five pairs, which would be a manifest absurdity. 
The genus was established by Latreille in the second 
edition of the ‘* Régne Animal,” published in 1829 
(having been indicated by name only in the ‘ Familles 
Naturelles,’”” published in 1825), for the reception of 
Idotea Baffini.* In 1834, Professor Westwood communi- 
cated a memoir, with figures, on the genus, which he 
regarded as osculant between the normal Jsopoda and the 
Lemodipoda of Latreille, to the Entomological Society 
of London. (Transactions, vol. i. p. 69.) He divided 
the genus into two sections (subsequently adopted by M. 
* Latreille gave the species under the undescribed name of A. tuberculatus, 
not recognizing its identity with 7. Bajini. Even now it is only by conjecture, 
or by the synonyms given by M. Milne Edwards, that we are able to identify 
the animal intended by Latreille. 
