187 



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. 

 Antenna 1 , 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 



