2 ART. 4. — EKITARO NOMURA : 



Before I enter into the subject of this paper I must express 

 my best thanks to Prof. Goto for his kind supervision and help- 

 ful advices. I must also note that the work was done in the 

 Zoological Institute of the Science College, Imperial University of 

 Tokyo. 



I have found three species of Limnodrilus among my collec- 

 tions of aquatic oligochastes, which were made in the gutters 

 and ditches of Tokyo and Morioka from July to November, 1910. 

 They differ distinctly from one another by the length of the 

 chitinous penis sheath. To be more precise, in Form A the 

 chitinous penis sheath is 3-4 times, in Form B 10-11 times, 

 and in Form C 30-33 times, as long as the diameter of the 

 proximal end. There were no intermediate lengths, and the three 

 forms differ moreover in several other points. 



The Form C does not come into consideration in the present 

 paper. The forms A and B must now be compared with L. 

 gotoi Hatai as to their systematic characters, which may be 

 shown, for convenience, as follows. 





Form A 



Form B 



L. gotoi Hatai 



Sperniathecee 



with 

 sperrnatophores 



without 

 spermatophores 



with 

 spermatophores 



Prostata 



spindle-shaped 



irregular shape 



spindle-shaped 



Penis sheatli 



3-4 times 

 as long as wide 



10-11 

 ditto 



? 10-11 

 ditto 



Ant. sperm- sac 



unpaired 



paired 



unpaired 



Post, sperm-sac 



XI only, unpaired 



XI-, unpaired 



XI-, unpaired 



! Setse 



i 



sigmoid with 

 ; unequal branches 



sigmoid 



with about equal 



branches 



sigmoid, 

 bifurcate 



The generic characters are not included in the above table. The 



