1877.] CRUSTACEA, CHIEFLY FROM SOUTH AMERICA. 663 



Of this small species but two specimens, in an imperfect condition, 

 are in the collection ; and although I dissected the mouth-organs of 

 one specimen, I failed to extract them in a sufficiently perfect con- 

 dition to admit of their description. The specimens were found in 

 a well. 



ISOPODA. 



The species of Isopoda described in the present paper belong to 

 the terrestrial or subaquatic ArmadillidcB and Oniscidce, and the 

 parasitic Cymothoidce. The species of the two former families have 

 been comparatively neglected by modern carcinologists, and many of 

 the continental species are known only from the short and insuf- 

 ficient descriptions of Brandt, Koch, and other authors, based mainly 

 upon differences of colour, which is often a very variable charac- 

 leristic in individuals of a single species, and, taken alone, will not 

 always suffice to identify the animals of this group. Probably better 

 characters are to be found in the punctulation and granulation of 

 the body, and the form of the antero-lateral lobes of the head and 

 of the segments of the body, and uropoda. 



On account of the brevity of many of the earlier descriptions, it 

 is very difficult, or even impossible, to institute comparisons between 

 the different species ; and, as stated above, I have only attempted to 

 do this, in the case of the American species, with others of the same 

 genera inhabiting the American continent. 



The mouth-organs, which in the Atnphipoda afford very valuable 

 characters for the distinction of genera, in the Isopoda (at least in 

 the terrestrial members of the order) do not present any marked 

 peculiarities of structure. M. Lereboullet, one of the best authorities 

 on the subject, has, in the abstract of his valuable memoir on the 

 OniscidcB of the environs of Strasbourg (Comptes Rendus, xx. 

 p. 346, 1849), even stated it as his opinion that they are in no case 

 available for characterizing the genera and species. 



Family Armadillid^. 

 Subfamily Armadillin^. 



Professor Brandt, in his subdivisons of this family, which are very 

 natural, and were adopted almost without modification by M. Milne- 

 Edwards in the ' Histoire naturelle des Crustaces,' makes two sub- 

 families — (a) Armadillidia, containing only his genus Armadillidium, 

 and (6) Oubaridea, including the genera Cuburis, Armadillo, and 

 Biploexochus. Unfortunately he restricts the genus Armadillo to 

 the single species A. officinalis, Dumeril, which had not been de- 

 scribed when Latreille founded the genus, and does not mention at all 

 the earlier A. vulgaris of Latreille, which, as described by Milne- 

 Edwards, Lereboullet, and other authors, belongs to his genus 

 Armadillidiu m . 



I therefore retain the name of Armadillo for those species in 

 which the terminal segment of the abdomen is truncate at the ex- 



