LIGIA. 67 
(ii) Pleopoda to a great extent branchial; the 
Uropoda valve like, inflexed, arching over the 
Pleopoda - - - . 3. Valviferae. 
(2) Uropoda terminal. (i) Pleopoda exclusively 
branchial, generally covered by a thin oper- 
cular plate (the modified Ist pair) - 4. Asedlota. 
(ii) Pleopoda for air breathing - 5. Oniscoidea. 
(iii) Pleopoda when present, exclusively bran- 
chial in the adult animal and not covered by 
an operculum - - - 6. Epicarida. 
Ligia oceanica belongs to the tribe Oniscoidea, which 
are characterised by being terrestrial. This tribe includes 
all the so-called ‘‘ wood-lice.” Their abdominal append- 
ages are fitted for air breathing, but in Ligia there is a 
very near approach to branchial respiration, as moisture 
is necessary. The body is oval in shape, and the seven 
pairs of thoracic appendages are similar in character. 
Ligia oceanica was first described in 1767 by Linnaeus 
as Oniscus oceanicus. Later, in 1798, the genus Ligza 
was created by Fabricius to include the Onzscus oceanicus 
of Linnaeus. 
Brouoey. 
Ligia oceanica (P1. I.) has a wide distribution, and 1s 
recorded from the coasts of the British Isles, Faroe Islands, 
Norway, Denmark, Germany, Belgium, France, Spain, 
Morocco and America. At Plymouth* I have found 
Ligia most numerous, and of the maximum size, on 
Drake’s Island. At Port Erin they occur in the cliff near 
the old biological station. 
* I wish to express my thanks to the Council of the Marine 
Biological Association of Great Britain for the use of a table at the 
Plymouth Laboratory, during the Easter vacation, 1906. Other 
material for this memoir was obtained at the Marine Biological 
Station, Port Erin, during the Easter vacations, 1903-4. 
