356 PROCEEDINGS OF THE NATIONAL MUSEUM vol. 112 



In figure 8 I have plotted the distribution of Parathemisto in the 

 vicinity of Japan from Irie's data. To these data I have added some 

 Albatross and Carnegie stations as well as the localities reported by 

 Nakai (1955). While the occurrences in the Japan and Okhotsk Seas 

 are undoubtedly P. japonica, those east of Japan probably include both 

 P. japonica and P. pacifica. Since the temperatures limiting south- 

 ward penetration are similar for P . japonica in the Japan Sea (see p. 366) 

 and for P. pacifica along the California coast, Irie's data on the occur- 

 rence of Parathemisto east of Japan can be applied to both P. japonica 

 and P. pacifica. His data show that these species are most abundant 

 north of Japan. Irie (1948) states that Parathemisto is abundant 

 between 40° and 50° N., common between 35° and 40° N., but very 

 rare between 25° and 35° N. Figure 8 indicates that the southern 

 boundary falls at about 36° N. 



P. pacifica inhabits cold water, and the extent of its southern pene- 

 tration along the eastern coast of Japan must depend on the relative 

 influences of the Kuroshio and the Oyashio. The warm Kuroshio 

 leaves the coast of Japan and turns east or northeast at Cape Inubozaki 

 (35°40' N.), with a variable amount of north-south meandering 

 (Masuzawa, 1955). Koizumi (1953) reported on the temperature 

 variations at 39° N., 153° E., a locality which is sometimes covered 

 with water of Kuroshio origin, at other times with cold water of Oya- 

 shio origin. Here the temperature at a depth of 25 m. in 1948 varied 

 from 10.80° C. in March to 21.64° C. in September. Clearly the 

 southern boundary of the Oyashio and of its inhabitants, including 

 P. japonica and P. pacifica, is subject to fluctuation. 



In the region where the two current systems meet, the Oyashio may 

 underlie the Kuroshio to a limited extent. Tanaka (1953) observed 

 that in the waters near the Izu Peninsula the warm-water copepod 

 species of the Kuroshio were confined to the upper 200 m., while the 

 cold-water species of the Oyashio were obtained chiefly from below 

 200 m. 



Recently several Russian biologists of plankton have set up faunal 

 zones and zoogeographic boundaries in the region east of Japan and 

 southeast of the Kurile Islands. This work is summarized by Beklem- 

 ishev and Semina (1956) and by Bogorov (1958). P. japonica (=P. 

 japonica + P. pacifica) is listed by Bogorov and Vinogradov (1955) 

 as an inhabitant of their boreal epipelagic zone, extending south to 

 about 40-42° N. and having surface temperatures of from 9-15° C. 

 This zone is also characterized by the copepods Calanus tonsus and the 

 chaetognaths Sagitta elegans and Eukrohnia hamata. Brodsky (1955a) 

 refers to it as the "Calanus tonsus Zone," and it undoubtedly corre- 

 sponds to Hida's (1957) "Subarctic Zone" in the mid-Pacific. 



