350 PROCEEDINGS OF THE NATIONAL MUSEUM vol. 112 



but very closely related species, which may be told apart by the larger 

 size, greater development of the pereopodal setae, and unequal anten- 

 nae of P. japonica. In addition to the small morphological differ- 

 ences, the two species have different geographical distributions. P. 

 japonica occurs in the Japan and Okhotsk Seas and in a limited region 

 east of Japan and the southern Kuriles; P. pacifica inhabits sub- 

 arctic water in the rest of the Pacific. 



The type material of P. pacifica consisted of 7 specimens, 3 females 

 and 4 males, taken at the surface at Challenger station 240 (32°20 / N., 

 153°39 / E.). Stebbing's description was based on a male which seems 

 not to be extant, for I am informed by Dr. Isabella Gordon (in litt.) 

 that the collections of the British Museum (Natural History) contain 

 3 females and 3 males but no dissected male. Through her kindness 

 I have been able to examine a male and a female with ova from the 

 Challenger material. The female, 6.7 mm. in length, has fully devel- 

 oped oostegites and subequal antennae 1 and 2. The male, measur- 

 ing 6.5 mm., is not fully mature, for the antennae are only slightly 

 longer than the height of the head. Since Stebbing did not select a 

 holotype, the Challenger specimens are all syntypes. The above ma- 

 ture female is herewith designated as the lectotype of P. pacifica. 



Color: Eyes red, with black centers. General body color purplish 

 red due to rather large, dark-red chromatophores, which are visible 

 through the transparent cuticle. The chromatophores are most abun- 

 dant on the pereon, and make it quite dark. Food in the gut may 

 add to the darkness of the pereon. On the pleon the chromatophores 

 occur slightly less than halfway down the sides of the pleonites and 

 on the middle of the dorsal surface of the third and sometimes also 

 the second pleonite. One or two chromatophores are located on the 

 dorsal surface of the peduncle of uropod 3. The mouthparts have a 

 reddish appearance. Pl-2 have a few chromatophores, and P3-4 may 

 have chromatophores at the distal end of the basipods. P5-7 are 

 without chromatophores. 



Distribution: The distribution of P. pacifica will be considered in 

 three sections: (1) in the area surveyed by CCOFI, off the coasts of 

 California and Baja California; (2) in the northwestern Pacific Ocean 

 adjacent to Japan and the Kurile Islands; (3) in the north Pacific 

 Ocean as a whole. 



1. CCOFI Area: Figures 4 to 7 show the distribution of P. pacifica 

 encountered during four CCOFI cruises. At the stations shown, ob- 

 lique hauls of 20 minutes duration were made with one-meter plankton 

 nets from a depth of about 70 m. (140 m. in cruise 20 except for the 

 northernmost line of stations) to the surface. Details of net construc- 

 tion and methods by which the hauls were made are given by Ahlstrom 

 (1948, 1952). The volume of water strained during a haul was meas- 



