LIGIA. 67 



(ii) Pleopoda to a great extent branchial; the 

 Uropoda valve like, innexed, arching over the 

 Pleopoda 3. Valviferae. 



(2) Uropoda terminal. (i) Pleopoda exclusively- 

 branchial, generally covered by a thin oper- 

 cular plate (the modified 1st pair) - 4. Asellota. 

 (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 Ligia 

 was created by Fabricius to include the Oniscus oceanicus 

 of Linnaeus. 



Biology. 



Ligia oceanica (PL I.) has a wide distribution, and is 

 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, 



