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subcheliform structure. None of the forms belonging to the present group lead
a parasitic existence. The group contains as yet 5 families, all of which arc re-
presented in the fauna of Norway. It is, however, very probable
found convenient to establish more families subsequently.
Fam. 1. Asellidae.
that it will be
Characters. Body more or less broad, depressed, with the lateral parts
of the segments lamellar. (Vphalon of moderate size, without any rostrum, lateral
parts scarcely expanded. Caudal segment large, shield-like. Eyes, when present,
small, lateral. Both pairs of antenna1 with multiarticulate flagella, the superior
ones much smaller than the inferior, and issuing close together. Oral parts nor-
mal. Legs ambulatory, except the 1st pair, which are distinctly subcheliform.
Pleopoda in female 4 pairs, the 1st being very small, not operculiform, consisting
each of a single rounded lamella; the 3 succeeding pairs biramous, with both
rami lamelliform, outer lamella of 2nd pair very large and incrusted, so as to
form, together with the corresponding lamella of the other side, a sort of oper-
culum, completely covering the 2 succeeding pairs. Pleopoda in male 5 pairs,
an additional very small pair, constituting the copulative appendages, being inter-
posed between the 1st and 2nd. Uropoda comparatively large, biramous, with
the rami styliform or lamellar.
Remarks. In the restriction here adopted, this family is chiefly charac-
terized by the structure of the pleopoda, which differs considerably from that
found in the other Asellota, Whereas in these, the 1st pair in the female are
invariably transformed to a single large opercular plate, completely covering the
succeeding pairs, this pair, in the forms belonging to the present family, are of
inconsiderable size and not at all opercular, forming 2 discrete, simple, setiferous
lamellae. On the other hand, the outer plate of the 2nd pair is very large and
incrusted, lying in close contact with that of the other side, so as to obtect
completely the 2 succeeding pairs. In the male, there is found, immediately behind
the 1st pair of pleopoda, an additional pair of very small biramous appendages,
of which no trace can be detected in the female, and which represent the copulative
organs. As regards the other Asellota, the male operculum is apparently split into
3 juxtaposed segments, one narrow median segment, which exhibits a well-marked