ISOPOD GENUS LIGIA. 687 



The moitth-parts differ slightly throughout the genus. It is 

 interesting to note that in the majority of species the maxillipede 

 (whose palp has always five separate or indicated joints) and 

 second maxilla differ from those of Ligia oceanica, the type of the 

 genus. The first maxilla and the mandible are, however, very 

 constant in structure, on which account I have considered it 

 unnecessary to deal with them under each species. 



The percBopods are always biunguiculate. In the males of certain 

 species the inner edges of the first and sometimes second and 

 third leg are deeply sulcate. I have not enough material to 

 pronounce on the value of this character, but as I have found it 

 present in some and absent in other specimens collected at the 

 same spot and obviously identical in all other particulars, I feel it 

 necessary to regard it with caution until its significance is known. 

 The sexual difierences have been alluded to above. 



I have not found the vleoijods to be of any systematic value. 



The uropods are frequently distinctive both in shape and size. 



(5) The genus Geoligia. 



This genus was founded by Dollf us in 1893 on a single' damaged 

 male specimen obtained from Valencia (Venezuela) at a height 

 of 1200 metres above sea-level. The character on which the 

 genus was separated from Ligia was the absence of indication of 

 separation of coxal plates from terga on the thorax, added to 

 the unusual habitat of the specimen. 



In 1900 the same author described specimens from the Hawaiian 

 Islands, obtained at heights varying from 2000 feet to 4000 feet, 

 as a new species of the same genus. These differed from the 

 holotype in many particulars, and one male specimen was in 

 possession of a complete uropod of extraordinary form, the rami 

 being composed of several segments. Dollfus accordingly added 

 to the characters of the genus the possession of jointed uropods, 

 and his diagnosis is as follows : — 



" Coxopodites (epimeres) non ou tres pen distincts. 

 Appendices des uropods articules. Le reste, et notammement 

 les parties buccales, comme dans le genre Ligia — especes 

 terrestres." 



An examination of the degree of separation of the coxal plates 

 from the terga throughout the genus Ligia reveals that it would 

 be a most treacherous character on which to found a species, 

 let alone a genus. It is variable, even within a species, but 

 a generalisation that would be true for the majority of cases 

 might be stated thus : — The sutures between the coxal plates and 

 terga are always visible to a greater or lesser extent in the 

 female on the second, third, and fourth thoracic somites: they 

 may be present or absent on the other somites. In the male the 

 svitures may be altogether obliterated (e. g. L. olfersii) or well 

 marked on each thoracic somite (e. g. L. oceanica). 



