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Remarks. This form was described as early as in the year 1778 by
De Geer as U-iiiscus convcxus. The Pored I to ar-maa'iUoides of Lereboullet is un-
questionably identical with it, and, according to B.-Lund, P. spinifrons of Brandt
and P. ItKt-is of Koch ought also to be referred to this species. It is easily
recognised from our other Oniscidse by its strongly convex body and its capa-
bility of being rolled up into a ball, in which respect it strongly
recalls the
species of the genus Armadillidium. The slender antennae and the very diffe-
rent structure of the uropoda, however, suffice at once to distinguish it from
that genus.
Occurrence. I have found this form not infrequently in the neighbourhood
of Christiania, as also at Drobak and Skien; and some specimens were, moreover,
sent to me by Mr. Ellingsen, who collected them near Kragero. It is gene-
rally found in rather dry situations, beneath stones, especially where the ground
consists of loose pebbles. It moves about rather quickly, but, when alarmed,
at once rolls its body up into a ball, which easily escapes the eye of the observer.
Distribution. Sweden, Denmark, British Isles, Germany, Bohemia, Hol-
land, Belgium, France, Turkey, Caucasus, North America.
Fam. 4. Armadillidiidae.
Characters. Body convex, contractile into a ball; integuments strongly
incrusted. Cephalon flanked by the side-plates oi the 1 st segment of mesosonie,
front sub-truncate, marginate, lateral lobes distinct, median lobe obsolete, epistome
vertical. Metasome not abruptly contracted, terminal segment short and broad.
, Antenna1
comparatively small, with the tiagellum biartieulate or triarticulate. Oral
parts of a similar structure to that in the Oniscidce. Legs comparatively short.
Opercular plates of all the pleopoda, or only of the 2 anterior pairs, provided with
air-cavities. Copulative appendages about as in the Onixcidce. Uropoda short,
not extending beyond the limits of the last segment and the epimeral plates of
the penultimate one. The young, on leaving their mother, have all the 7 segments
of mesosome distinctly defined.
Remarks. The present family agrees in most points rather closely with
that of the Oniscidce, and it is somewhat questionable, if it should in reality be
kept apart, as there are transitory forms between the two families, e. g. the