6 ABÏ. II. — A. IZÜKA : 



beyond that island. The southern hmit of Nereis mictodonta, N. 

 cuUrifera, N. cylindrata, Polyno'è clava, P. vexillaria and Cerato- 

 cephale osaioal seems to be Kyushiu Island. 



Thus, numerous species of the Polychaeta cease to occur far- 

 ther south than Satsuma, so that the southern end of Kyushiu 

 may be considered to constitute an important boundary line in 

 regard to their distribution. 



On the Pacific Ocean side, many of the warm-sea forms 

 cease to occur in the region north of Kinkwasan Island, while 

 the cold- sea forms seldom extend southward beyond the same 

 island ; hence Kinkwasan Island may be taken as the limit be- 

 tween the two. On the Japan Sea side, Prov. Uzen seems to be 

 the northern limit of Avarm-sea forms, while Prov. Osliima in the 

 Hokkaido or Prov. Mutsu at the northern end of Honshiu appears 

 to be the soutliern limit of cold sea forms. 



Accordingly, in regard to the distribution of marine annelids, 

 the littoral zone of Japan may be roughly divided into the follow- 

 ing sections and subsections : 

 Sect, A, Japau Sea side. 



Subsect. 1. From Prov. Cliikuzen in Kyiisliiu to Oga peninsula in 

 the north of Plonshiu. 

 ,, 2. From Oga peninsula to Sakhalin. 

 Sect. B. Pacific Ocean side. 



Subsect. 1. From the Knriles to Kinkwasan Island in Prov. 

 Rikuzen. 

 ,, 2. From Kinkwasan Island to the southern end of 



KyusLiu. 

 ,, 3. From the soutliern end of Kyushiu to Formosa. 

 It win bo seen that the above sections and subsections of the 

 httoral zone of Japan stands in relation to the distribution of ocean 

 currents, both warm and cold, that sweep along the coasts of Japan. 



