NO. 1989. A8CIDIAN8 FROM NORTHEASTERN PACIFIC— RITTER. 431 



Considered with reference to distribution in different parts of the 

 Pacific Ocean, we get 



TABLE 3. 



Table 3 brings out the sharpness with which the Bering Sea is 

 separated from the main Pacific Ocean as an ascidian province. 



There is doubt as to what province species occurring on the south 

 as well as on the north shores of the Aleutian Islands should be 

 assigned. The principle I have followed is that species like Dendro- 

 doa tuhercvlata, which are abundant in Bering Sea and are unknown 

 southward except along the south shore of the Aleutian chain, should 

 be counted as exclusively Bering Sea species. 



On the other hand, Culeolus sluiteri, for example, is assigned to 

 south of Bering Sea only, though it occurs near the Aleutian Islands, 

 but on the south side. Only more extensive collecting can resolve 

 these questions. 



