185 



outer. Colour of dorsal face light reddish brown, the segments of mesosome 

 being bordered behind with darker brown, and having on each side of the median 

 line a group of lighter dots or stripes; antennae banded with white. Length of 

 adult female 9 mm. 



Remarks. This form has more generally been recorded under the specific 

 name maculicornis proposed by Koch; but, as the name pruiiiosus is the older one, 

 it ought certainly to be retained. Some other synonyms are quoted above. It 

 is easily recognizable by the oblong, flattened body, the abruptly contracted meta- 

 some, and the long and slender antennae, in these points somewhat resembling 

 Philoscia muscorum, from which, however, it is at once distinguished by the bi- 

 articulate antennal flagellum. 



Occurrence. I have met with this form not infrequently in the immediate 

 vicinity of Christiania, especially in refuse-heaps, together with PorceUio scaber; and 

 it has also been found by conservator Storm in similar situations at Trondhjem. 

 It is a very agile animal, running about with great rapidity when disturbed; 

 and, as the integuments are very thin and soft, it is easily injured when 

 being captured, unless great care be exercised. 



Distribution. Greater part of Europe, North Africa, North and South 

 America, Sumatra, Madagascar, etc. 



Gen. 6. CyliStleUS, Schnitzier, 1853. 



Generic Characters. Body oblong, very convex, capable of being rolled up 

 into a perfect ball, integuments rather hard. Cephalon with the lateral lobes distinct, 

 median lobe very small or obsolete. Side-plates of [mesosome large, those of 

 1st segment the largest. Metasome not abruptly contracted, epimeral plates 

 of 3rd to 5th segments well developed, recurved ; last segment conically produced 

 behind. Eyes distinct, lateral. Antennulse with the last joint conically produced. 

 Antennae long and slender, with the flagellum biarticulate. Oral parts of a similar 

 structure to that in Porcellio. Legs of moderate size, successively increasing in 

 length behind. Opercular plates of all the pleopoda provided with air-cavities. 

 Copulative appendages of male of a similar structure to that in J'urcrlfio. Uropoda 

 rather much produced, especially in male ; inner ramus very narrow, and issuing far 

 in front of the outer. 



21 Crustacea. 



