362 ARCTURID^. 



cluiracter 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 EdrioiMhahna, 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 *' Regiie Animal," published in 1829 

 (having been indicated by name only in the " Families 

 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 Isopoda and the 

 Lcemodipoda 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. tuherculafus, 

 not recognizing its identity with 7. Baffini. Even now it is only by conjecture, 

 or by the synonyms given liy M. Milne Edwards, that we are able to identify 

 the animal intended by Latreille. 



