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Show 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 condition 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 Armadillidee 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 insufficient descriptions of Brandt, Koch, and other authors, based mainly upon differences of colour, which is often a very variable characteristic 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 Amphipoda 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 Oniscidce 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 ARMADILLIDJE. Subfamily ARMADILLIN^E. 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 subfamilies- (a) Armadillidia, containing only his genus Armadillidium, and (b) Cubaridea, including the genera Cubaris, Armadillo, and Diploexochus. 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 A y/yij ft fl'l Iff (£1 J/ JM I therefore retain the name of Armadillo for those species in which the terminal segment of the abdomen is truncate at the ex- |