368 PROCEEDINGS OF THE NATIONAL MUSEUM vol. 112 



plained as being derived from the Japan or Okhotsk Seas. For some 

 as yet unknown reason, P. japonica has not been able to extend its 

 range far beyond the immediate vicinity of its site of origin. 



Parathemisto (Parathemisto) abyssorum Boeck 



Figure llj'-fc; 12-13 



Parathemisto abyssorum Boeck, 1870, p. 87(7). — Barnard, 1959, pp. 125-127, 



pis. 17-19. 

 Themisto abyssorum (Boeck), Stephensen, 1923, pp. 20-24, chart 4; 1924, pp. 95-97, 



figs. 36-38; 1944, p. 12.— Shoemaker, 1930, pp. 132-133; 1955, p. 72. 



Diagnosis: Length of adult 10-21 mm. Larger and more slender 

 than P. pacijica, and head more roundly produced. Maxilliped with- 

 out a distal row of setae on the basal plate. Pi -4 with more surface 

 setae than in P. pacijica; posterior margin of propodus of Pi serrate 

 and bearing several long setae. Carpal process of P2 with long end 

 spine. In length P5>P7>P6; no long spines at posterior distal 

 corners of carpi; dactyls not pectinate. Peduncle of uropod 3 about 

 3 times as long as telson. 



Distribution: Ekman (1953, p. 340) mentions P. abyssorum as 

 an example of an "arctic-bathy-subarctic" species. In this category 

 he includes plankters which live primarily in Arctic waters, but are 

 also found in deep water in lower latitudes. A detailed discussion of 

 the distribution of P. abyssorum in the Atlantic is given by Stephensen 

 (1923, pp. 22-24, chart 4). Found throughout the Arctic and Sub- 

 Arctic Atlantic, it is very common in the vicinity of Greenland 

 and between Norway and Iceland. Stephensen believes that 

 Bonnier 's (1896) record of 9 mm. ovigerous P. oblivia taken at a depth 

 of 950 m. in the Bay of Biscay should be referred to this species. On 

 the western side of the Atlantic it occurs occasionally in the Gulf of 

 Maine (Bigelow, 1926) and is widely distributed in and around the 

 Gulf of St. Lawrence (Shoemaker, 1930; Bousfield, 1951). Bousfield 

 believes that the permanent deep layer of very cold water in the Gulf 

 of St. Lawrence enables the species to breed there successfully, as 

 evidenced by the large numbers of young and immature stages taken 

 near the surface. 



I have not found P. abyssorum in any plankton collections from the 

 Pacific Ocean. It was, however, the most commonly collected amphi- 

 pod during the 1950 and 1951 expeditions of the Burton Island to the 

 Beaufort Sea and in the 1953 expedition to Amundsen Gulf and Prince 

 of Wales Strait. Station positions and locality records for P. abys- 

 sorum are shown in figure 12. Plankton hauls were made vertically 

 with a one-half-meter Nansen type plankton net. In 1950 the hauls 

 were made from various depths, usually 100-0 m., and in 1951 all 



