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The mandibles are strong, and always without palps. The anterior maxillae are
normal, with 2 masticatory lobes, the inner of which carries on the tip
2 or 3
brush-like setse. The posterior maxillae, on the other hand, exhibit a rather dif-
ferent appearance from those in most other Isopoda, being laminar, with only a
very slight indication of a subdivision into lobes. The maxillipeds do not completely
cover the other oral parts, and they have the terminal part more or less reduced.
The marsupial pouch in the female is composed of 4 pairs
of broad lamellae is-
suing from the bases of the 2nd to 5th pairs of legs. The appendages of the
metasome are 6 pairs, the 5 anterior of which are respiratory in character,
the inner plate being of a very delicate spongy structure, whereas the outer is
more strongly chitinized and covers the inner like an operculum. In some cases
this opercular plate contains on the 2 anterior pairs, more rarely on all the
pairs, air-cavities or pseudo-trachese. In the male, the inner plate of the 2nd,
and often also of the 1st pair, is peculiarly modified, to serve for copulative
purposes. The last pair of appendages represent the uropoda. They are, as a
rule, birarnose, with the rarni uniarticulate, and they project more or less behind.
The forms belonging to this tribe are generally found in damp situations,
beneath leaves, stones or timber, often in great numbers, and feeding, it would seem,
on both animal and vegetable matter. They all seem to avoid the full light
of day, and some forms even lead a true subterranean existence, in which
case the eyes are often found to be rudimentary or wholly absent. As to the
respiration, it cannot properly be said to be an exclusive air-breathing in the same
sense as in insects. It is in fact to some extent branchial, and therefore a certain
amount of atmospheric moisture is indispensable to their existence. It is for this
reason, that in very dry weather these animals seem almost wholly to disappear,
retiring more or less deeply into crevices and hollows, where some moisture still
remains.
The tribe has been divided into 2 sections, viz., the LigicB and the
Onisci. Both of these sections may conveniently
be subdivided into several
families. Of such families 4 are represented in the fauna of Norway, and will
be treated of below.
Among the several authors, who have made the present tribe their
special study, must be named the Danish zoologist, Mr. Budde-Lund, who in his
admirable work, "Crustacea isopoda terrestria", has treated of all species at that
time known, both indigenous and foreign, amounting in all to several hundreds.
It is to be regretted that this valuable work is accompanied by no figures.