THE BRITISH WOODLICE. 17 
Classification.—The various genera of woodlice are con- 
nected together so closely, by intermediate forms, that their 
division into families is, to a very great extent, arbitrary. Bate 
and Westwood described but a single family Oniscide (1), 
though they distinguished two sub-families :—Ligiine, which 
included the forms with many joints to the flagellum of the 
antenna, and Oniscinz, which contained the rest. 
Since then the pill-woodlice have been thought by some to 
be sufficiently different from the other genera to warrant their 
separation, and three families namely, Ligiida, Oniscidz, and 
Armadillida have been recognized, as for instance by Dr. 
Scharff (63). 
A fourth family—Trichoniscide—has been added by 
Professor G. O. Sars, who in his Crustacea of Norway (59) 
alludes to the division of the tribe into the sections Ligie and 
Onisci and has adopted the following classification :— 
Orderv--ISOPODA. 
Tnbe—ONISCOIDA. 
Family I,—Licupae. Family III.—Oniscip&, 
Ligia. Oniscus. 
Ligidium. Philoscia. 
Platyarthyus. 
Porcellio, 
Metoponorthus. 
Family II. —TRIcHONISCID&. Cylisticus 
Trichoniscus. 
Trichoniscoides. Family 1V.—ARMADILLIDIIA. 
Haplophthalmus. Arvmadilidium. 
All the genera described by Professor Sars are represented 
in the British Isiands. 
Below is a scheme of classification and synopsis of the 
characters of British genera of woodlice which we have compiled 
in order to render easy the determination of the genus to which 
any particular specimen may belong. 
