ON THE ISOPOD GENUS LIGIDIUM. 823 



40. A Revision of the Isopod Grcnus Ligidium (Brandt)* 

 — Crustacea. Bj Harold Gordon Jackson, F.Z.S., 

 Birkbeck College, University of London. 



[Received July 13, 1923 : Head November 6, 1923.] 



(Text-figures 1-10.) 



Contents. 



Pago 



(1) Ititi'oductioii , , 823 



(2) (Generic and Specific Characters 824 



(3) Key to the genus ij^jriiiMw ., ' 828 



(4) 'V\w ^cwvin Ligidiiim 828 



1. Lirjidfum hi/pnornm 829 



2. Lifjidinm fragile 83l 



3. Liigidiiim gracile 832 



4. IJgidium latum 834 



o. Jjigidittm gennaniciim 835 



G. Ligidium japonicum 836 



7. Ligidium bosniense ■ 837 



8. Ligidium nodulosum 837 



9. Ligidium longicaudatum 838 



10. Ligidium {Typldoligidium) cceeum : 838 



(1) Introduction. 

 Tlie genus Ligidium was separated from Ligia by Brandt in 

 1833 with this dingnosis : " Articulus appendicis caudalis apicalis 

 exterior articnli basalis apici interius autem processui proprio 

 K3X articuh'. basalis apice prodeunti insertus." It is well defined 

 in structure and habitat from Ligia, although nearer to that 

 genus than to any other Terrestrial Isopod and linked to it by 

 the newly-described genus Ligidioides Wahrberg (1922) ; and 

 there is but slight range of structure within it. Budde-Lund 

 (1885) gives five species which he describes in Latin with the 

 utmost brevity and without figures. The most important and 

 indeed often the only character given is the form of the 

 uropod, but as the appendage is brittle and often lost, it is 

 sometimes impossible to make a certain identification from his 

 description. I only retain two of these species, but several 

 good species have been added since Budde-Lund's work, and his 

 collection contnins specimens, mostly unidentified by him, which 

 have enabled me to describe all but four species. The revision 

 of this genus has been greatly aided by a recent paper by YerhoefF 

 (1918) dealing with the European species, in which much-needed 

 new characters are proposed, and a newr subgenus, Ti/phloligidium, 

 is set up, on, to my mind, amply sufficient grounds, to contain 

 •Carl's cave-dwelling Ligidium caecum. 



* This paper is the second of a series; 



54* 



