the Species o/Limnoria. 



387 



Notwithstanding these many points of resemblance, there 

 are, however, some minute characters by which most of the 

 species can be distinguished. The most important of these 

 seem to me to be the characters of the mandibles and the 

 maxillipeds. The exact relationships of the species seem 

 rather difficult to disentangle, but the species may readily be 

 distinguished in the following way : — 



Artificial Key to the Species. 



Y I Palp of mandible two-jointed L. segnis. 



I I'alp of mandible three-jointed. 2. 



iEpipod of maxilliped shorter than second 

 „ JP"^^ • • • L. lipionim. 

 -Lpipod of maxilliped longer than second 

 joint. 3. 



3- j S^^j-^' ^.'^^ prominent tubercles on pleon Z. japonica. 



I JJod\' without prominent tubercles on pleon. 4. 



f 1^*^'^"°°^'^ of uropoda shorter than inner ramus. L. a?idrewsi. 

 4.-' Peduncle of uropoda longer than inner 

 (. ramus. 5. 



g_ \ Both rami of uropods very short Z. antnrcticci. 



I inner rami of uropods not very short Z. lyfefferi. 



^ The order in which the species are given in this artifi- 

 cial key does not correspond with their true relationships ; 

 the following tree represents my idea of their probable origin 

 —the position of L. japonica is, however, uncertain, as no 

 dehnite information as to its mouth-parts is available :— 



L. segnis. L. antarctica. L. pfefferi. L. andrewsi. L. lignomm. L. japonica. 



It is always important to connect the characters by which 

 species of a genus are related to one another with their 



27* 



