Introduction 1 Geological history 1 External structure and appendages 2 Alimentary canal 6 Circulatory system 7 Excretory system 7 Nervous system 8 Reproductive organs 8 Development 9 Habits and Economic considerations 12 Local names 15 Methods of collections and preservation 16 Classification 17 Scheme of classification and synopsis of generic characters 18 British Species 19 Section--Ligiæ 19 Family--Ligiidæ 19 Genus--Ligia Fabricius 19 _Ligia oceanica_ Linzé 19 Genus--Ligidium Brandt 21 _Ligidium hypnorum_ Cuvier 21 Family--Trichoniscidæ 22 Genus--Trichoniscus Brandt 22 _Trichoniscus pusillus_ Brandt 22 _Trichoniscus vividus_ Koch 23 _Trichoniscus roseus_ Koch 24 Genus--Trichoniscoides, Sars 25 _Trichoniscoides albidus_ Budde-Lund 25 Genus--Haplophthalmus Schobl 26 _Haplophthalmus mengii_ Zaddach 26 _Haplophthalmus danicus_ Budde-Lund 27 Family--Oniscidæ 27 Genus--Oniscus Linné 27 _Oniscus asellus_ Linné 27 Genus--Philoscia Latreille 29 _Philoscia muscorum_ Scopoli 29 _Philoscia couchii_ Kinahan 30 Genus--Platyarthrus Brandt 30 _Platyarthrus hoffmannseggii_ Brandt 30 Genus--Porcellio Latreille 32 _Porcellio scaber_ Latreille 32 _Porcellio pictus_ Brandt and Ratzeburg 33