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suture along the middle, and 2 lateral segments
of a more or less oval form,
and carrying inside 2 peculiar movable appendages (see PI. XL and succeeding).
A closer examination of this compound operculum will, however, soon show, that
the suggestion at first put forward by Dr. Hansen is quite correct. According
to the opinion of this distinguished carcinologist, the male operculum is more
properly composed of 2 pairs of successive appendages; the median piece repre-
senting the 1st pair of pleopoda, and accordingly answering to the female oper-
culum. whereas the lateral pieces represent the copulative appendages peculiar
only to the male. By such an explanation, indeed, more uniformity is obtained,
as to the number of appendages of the metasome, which, in fact, is the very
same in all Asellota, viz., 4 pairs in the female, and 5 pairs in the male, the
additional pair constituting the copulative appendages. In any case, however, the
structure of the 2 first pairs in the forms here treated of, is very anomalous,
and the remaining pairs are also rather different in appearance
from those in
other Asellota, thus justifying the establishment of a distinct family. This family
comprises as yet 4 genera, viz.. AscUu*. Mancasellus, Ccecidothea and Stenetrium,
all, except the last-named, containing exclusively fresh-water species. Of these
4 genera, only the first is represented in the fauna of Norway.
Gen. AsellUS, G. St. Hillaire, 17(34.
Generic Characters. Body broad, depressed, with the lateral parts of the
segments simple, not laciniate. Cephalon not very large, rounded,
front, lateral faces convex. Caudal segment very broad, slightly produced
tip. Eyes, when present, very small, consisting
elements. Superior antenme scarcely longer than the peduncle
truncated in
at the
of a limited number of visual
of the inferior
ones, the latter slender and elongated, without any outer appendage to the pe-
duncle. Mandibles with a well developed palp, molar expansion thick, subcylindric
1 in form. Second pair of maxilla with
the outer lamella? broad, laminar, and
edged with numerous curved and coarsely denticulated spines. Maxillipeds having
in female at the base a posteriorly pointing setous lappet, epignath broad, edged
witli bristles. 1st pair of legs with the carpus very small, propodos much larger
and broader in male than in female. The succeeding pairs rapidly increasing
in length, and having the carpal joint well developed, propodal one linear, dac-
tylus spinulose inside. Uropoda with the rami subequal, slender, styliform.
Remarks. This genus was established as early as in the year 1764 by
Geoffroy St. Hillaire. and may accordingly be regarded as the type of the family.