388 On the Species o/Limtioria. 



geographical distribution, and, in the case of Limnoria, it 

 seems possible to find some connection between the species 

 and their distribution. Tlius L. segnis, which lias probably 

 been long separated, geogra])hically, from the other species, 

 is distinctly marked off from them by its very small two- 

 jointed mandible. L. lignoriim^ which is found in the north, 

 also far removed from most of the other species, shows dis- 

 tinct differentiation from them in the small size of tlie epipod 

 of the maxillipeds; of L.Japonica we have unfortunately no 

 information as to the mouth-])arts, but from the description- 

 it appears that it is closely related to L. lignorurn, differing 

 only in tiie possession of tubercles on the pleon, and it may 

 be anticipated that its mandible will be found to be tliree- 

 jointed and the epipods of the maxillipeds to be short ; it 

 comes from Japan, not so very far from the Pacific Coast of 

 America, from which L. lignorurn has been recorded. The 

 remaining three species seem more closely connected with 

 one another, both in structure and in distribution ; there 

 is little essential difference in their moutli-parts, and it is 

 difficult to say whether they can continue to be considered as 

 distinct species when forms from intermediate localities have 

 been found. L. antarciica appears to be fairly well marked 

 off from the other two ])y the small size of both rami of the 

 inopoda, and L. andrewsi may be distinguished from 

 L. lifcfferi by the shortness of the peduncle of the uropoda ; 

 though these characters are proportional only and may 

 perhaps be found to vary with the age of the specimen. 



All the species, except L. segnis and L. antarctica, appear 

 to be wood-borers, and it seems likely therefore that the 

 wood-boring habit is characteristic of the whole genus and 

 that some of the characters of tlio animal, such as the small 

 size of the body and the shortness of the antennaj and the 

 peraiopoda, are associated with the wood-boring habit. The 

 wide distribution of the various forms and their small amount 

 of difference may therefore bo accounted for by their dis- 

 persal by means of floating logs into which they were boring ; 

 if this is so, then the two species which are not now wood- 

 borers must have lost the wood-boring habit through being- 

 cast on some shore where wood for boring was not avai]a!)i(', 

 and having had to ada})t themselves to another mode of life. 

 It is possible tiiat this occurred on the Antarctic Continent, 

 and that L. segnis lias reached New Zealand by way of the 

 Antarctic Continent, and in doing so has had the mandibuhir 

 ])alp more reduced than it is in L. antarctica (ihe species to 

 which it is ])robaljly most nearly allied) and in the species 

 liviiiif in the Indian Uce;ui. 



