56 THE BRITISH WOODLICE.
SCHEME OF CLASSIFICATION AND SYNOPSIS
OF GENERIC CHARACTERS.
Order—ISOPODA.
Tribe—ONISCOIDA.
Section I.—LIGIAE.
The Two Divisions of the Tail Appendages alike in Shape.
(A.)—Flagellum with 10 or more joints; tail appendages
wholly visible ; head without lateral lobes . Ligiidae.
(1.)—Abdomen broad ; body large; habitat
the sea-shore . . . . Ligia.
(2.)—Abdomen narrow; habitat wet moss . Ligidium.
(B.)—Flagellum with less than 10 joints ; head with
small lateral lobes, tail appendages partly covered Trichoniscidae.
(3.)—Abdomen narrow ; eyes compound ;
flagellum usually with more than 3
joints .... Trichoniscus.
(4.)—Abdomen narrow ; eyes simple or want-
ing; flagellum with 4 joints . . Trichoniscoides.
(5.)—Abdomen broad (comparatively); eyes
simple; back with longitudinal;
ridges ; flagellum with 3 joints . Haplophthalmus.
Section II.—ONISCI.
The Outer Divisions of the Tail Appendages Broader than the Inner.
(A.)—Tail appendages projecting when the animal is
walking ------ Oniscidae
(a.)—Unable to roll up into a complete ball.
(6.)—Flagellum with 3 joints; abdomen
broad ; head, with lateral lobes . Oniscus.
(7.)—Flagellum with 3 joints; abdomen
narrow; head without lateral lobes . Philoscia.
(8.)—Flagellum with 1 joint; eyes wanting ;
abdomen broad ; habitat, ant's nests Platyarthrus.
(9.)—Flagellum with 2 joints; abdomen
broad ; frontal lobe projecting . Porcellio.
(10.)—Flagellum with 2 joints; abdomen
narrow .... Metoponorthus.
(b.)—Able to roll up into a complete ball.
(11.)—Flagellum with 2 joints ; antennae
folded together over the thorax when
the animal is rolled up into a ball . Cylisticus.
(B.)—Tail appendages not projecting when the animal
walking ..... ARMADILLIDIIDAE.
(12.)—Flagellum with 2 joints ; antennae
hidden or carried at the sides of the
head when the animal is rolled up
into a ball .... Armadillidium.
[To be continued.]