From the genus _Porcellio_ the species with which we are concerned is at once distinguished by the three jointed flagellum. _Porcellio_ has but two joints and has, besides, a prominent lobe projecting from the middle of the head, which is not seen in _Oniscus_. _Philoscia_, although it has three joints to the flagellum, has a narrow abdomen and lacks entirely the lateral lobes which are a feature of the other genera of Oniscidæ. _Oniscus fossor_ of Koch (34) was recognized by Kinahan and by Bate and Westwood as a species. Dr. Scharff submitted specimens to Professor Budde-Lund who found no differences between them and _Oniscus asellus_. The former (63) mentions, however, that the characteristics of the supposed species are those of young examples of _Oniscus asellus_, and Professor Sars (59, p. 173) seems to be of the same opinion. Many young examples of _Oniscus asellus_ that we have examined have a curious whitish transverse band owing to the light colour of the dorsal plates of the first abdominal segments. The flagellum also does not seem to shew in young animals a distinct division into three joints. [Illustration: FIG. 43.--FLAGELLUM AND LAST PEDUNCULAR JOINT OF THE ANTENNA OF _Oniscus asellus_.] _BRITISH LOCALITIES:--_ _England_: High Beach, Epping, including an albino; Maldon; Brightlingsea; Iver; Hanwell; Eton; Kew; Pamber Forest; Kingston-on-Soar; Bluebell Hill, Maidstone; (W.M.W.): Lynmouth; (W.M.W. from J.T.C.). _Scotland_: (Scharff, 63). Dinnet, Aberdeenshire; (W.M.W. from Madame Christen). _Ireland_: (Scharff, 63). Yellow form with black spots, Donegal (R.W.) _FOREIGN DISTRIBUTION:--_ _Europe_: Almost throughout; (12): France; (25): Spain; (12): Sweden Norway; Denmark; Germany; Holland; Italy; Iceland; (59): Faroe Islands; Thorsharn; (R.F.S.) _Africa_: Azores; (24). _America_: Greenland; (59): North America; (Budde-Lund). _Genus_--=PHILOSCIA= Latreille, 1804 (37), p. 43. _Flagellum with three joints; abdomen narrow; head without lateral lobes._ If any further differences of an obvious kind be required to distinguish _Philoscia_ from _Oniscus_, one at least will be found in the much greater development of the hinder legs in the former genus. =Philoscia muscorum= Scopoli. PLATE X. [Not of Lereboullet, which is an _Oniscus_, see Bate and Westwood (1).] 1763 _Oniscus muscorum_ Scopoli (67), p. 415. 1793 _Oniscus sylvestris_ Fabricius (26), p. 397. 1793 _Oniscus agilis_ Koch in Panzer (51), part 9, pl. XXIV. 1833 _Philoscia marmorata_ Brandt (3), p. 183. 1838 _Ligia melanocephala_ Koch (34), part 22, pl. XVIII. 1847 _Zia melanocephala_ Koch (38), part 40, pl. I. p. 212. 1868 _Philoscia muscorum_ Bate and Westwood (1), p. 450. 1898 _Philoscia muscorum_ Sars (59), p. 174, pl. LXXVI., fig. 1.