344 DISCOVERY REPORTS 



with the layering between 250 m. and 100 m. at station WS 986 (08.05-14.07 hr.), indicates that the 

 animals concentrate around 250 m. in the daytime. Evidence of the vertical migration of a very closely 

 allied species, N. difficilis, and its possible relation to sonic scattering layers in the Pacific has been 

 presented previously (Boden, 1950a). 



Thysanoessa gregaria G. O. Sars 

 Thysanoessa gregaria G. O. Sars, 1883, p. 26. 



Table 6. Occurrence of Thysanoessa gregaria 



This species is usually quite common in this area (Boden, 1954). Its worldwide distribution is of 

 an antitropical nature (Hubbs, 1950, 1952), although Tattersall (1926) claims that it is common in the 

 deeper waters in the tropical oceanic area. This leads to an attractive speculation that the apparent 

 tropical discontinuity of distribution may be associated with a submergence along temperate iso- 

 therms. Actually Tattersall's and Moore's (1952) records are not below 28 N. Brinton (Scripps Inst, 

 of Oceanography — personal communication) finds that the species actually does seek deeper waters 

 toward the tropical limits of its range. The limited number of deep hauls which he has made in the 

 equatorial regions of the Pacific, however, have not yielded any specimens of T. gregaria and he is of 

 the opinion that it is a true antitropical species. 



Nematobrachion boopis Caiman 



Nematodactylus boopis Caiman, 1896, p. 17; Nematobrachion boopis Caiman, 1905, p. 153. 

 Two adult females were captured between 750 m. and 500 m. at station WS 976. 



Stylocheiron maximum Hansen 

 Stylocheiron maximum Hansen, 1908a, p. 92. 



Two larvae of this species were taken, one at the 250-100-m. level at station WS 976 and the other 

 in the upper 50 m. at station WS 986. At station WS 997 an adult female was taken between 100 m. 

 and 50 m. and another between 500 m. and 250 m. 



