134 PROCEEDINGS OF THE NATIONAL MUSEUM. 



3. The form of the antero lateral angles of the first thoracic segment. 

 In I. ochotensis these angles are markedly truncate, while in the 



present species they are rounded. 



4. The narrower epimera in I. japonica. 



5. The shape of the terminal segment. 



In /. ocJiotensis the lateral margins of this segment are concave, the 

 lateral angles prominent and rectangular, the median posterior tooth 

 or apex not greatly produced, while in I. japonica the lateral margins 

 are straight, the lateral angles less prominent and obtuse, and the 

 median posterior tooth or apex greatly produced, being twice the length 

 of that in I. ochotensis. 



6. The more slender and shorter legs of I. japonica. 



7. The differently shaped opercular valves. 



8. The more slender joints in the first pair of antennae of J. japonica. 



