_Porcellio_ is easily separated from the previous genera--_Oniscus_, _Philoscia_, and _Platyarthrus_--by its two-jointed flagellum. The fact that the abdomen is not abruptly narrowed separates it from _Metoponorthus_, which also lacks the prominent frontal lobe so characteristic of _Porcellio_. The species of this genera might be confused with _Cyclisticus_ which has two joints to the flagellum and a broad abdomen, but the latter genus has the power of rolling itself into a ball, while its frontal lobe is very small, and the first segment of its thorax is comparatively larger than in any species of _Porcellio_. =Porcellio scaber= Latreille. PLATE XIII. 1804 _Porcellio scaber_ Latreille (37), p. 45. 1818 _Oniscus granulatus_ Lamark (36), p. 261. 1818 _Porcellio nigra_ Say (62), p. 432. 1840 _Porcellio brandtii_ Milne-Edwards (46), p. 168. 1840 _Porcellio dubius_ Koch (34), part 34, pl. VIII. 1847 _Porcellio asper_ Koch (35), p. 207, pl. VIII., fig. 98. 1857 _Porcellio montezumæ_ Saussure (60), p. 207. 1865 _Porcellio paulensis_ Heller (31), p. 136, p. XII., fig. 5. 1868 _Porcellio scaber_ Bate and Westwood (1), p. 475. 1876 _Porcellio graniger_ Miers (44), p. 223. 1885 _Porcellio graniger_ Budde-Lund (8), p. 149. 1898 _Porcellio scaber_ Sars (59), p. 176, pl. LXXVII. The body of _Porcellio scaber_ is densely covered with tubercles. Its colour is usually of a very dark grey, but at times it is quite red or variegated with yellow. Albino specimens have been recorded. The two joints of the flagellum are of the same length and together equal that of the last joint of the peduncle. Air-tubes are present in the outer plates of the first two abdominal appendages. [Illustration: FIG. 47.--FLAGELLUM AND LAST PEDUNCULAR JOINT OF THE ANTENNA OF _Porcellio scaber_.] _BRITISH LOCALITIES:--_ _England_: High Beach, Epping; Warley; Brightlingsea; (W.M.W.): Maldon; (W.M.W. from R.M.): Langley; Kew; Skirmett; Pamber Forest; (W.M.W.): Liphook; (C.S.): Stoke-on-Trent; Kingston-on-Soar; (W.M.W.) _Scotland_: Dinnet (W.M.W. from Madame Christen). _Ireland_: Common everywhere; (Scharff, 63.) _FOREIGN DISTRIBUTION:--_ _Europe_: Throughout; (59): France; (28): Spain; (15): Iceland; (59): Faroe Isles--Thorsharn and Naalsoe--(R.F.S. and B.M., N. Annadale). _America_: Greenland; North America; Sandwich Isles; (B.M.); Mexico; (59): St. Paul; St. Croix; (59); Ascension; Tristan d'Acunha; (23) _Asia_: Ceylon; Kamtschatka: (23). _Australia_: Melbourne; Sydney; Tasmania; New Zealand; (B.M., Chilton). _Africa_: Azores; Canaries; Cape of Good Hope; (24). =Porcellio pictus= Brandt and Ratzeburg. PLATE XIV.