DISCUSSION OF SPECIES 



193 



it sometimes migrates to the surhue at night. This species 

 has apparently been recorded only by Giesbrecht (1892, 

 p. 359) and Wolfenden (1911, p. 523). 



Genus MACROSETELLA A. Scott, 1909 



Macrosetella gracilis (Dana) 



\Sftella gracilis Dana, Proc. Amcr. Acad. Arts and Sci., vol. i, 

 p. 154, 1847; U. S. Exploring Exped., 1838-1S42 (Wilkes), 

 vol. 14, pt. 2, Crustacea, p. 1198, 1853; pi. 84, fig. ^d-g, 1855.] 



Found at nearly every station in the Atlantic south of 50° 

 north latitude, and in every region of the Pacific with 

 numerous gaps in the distribution. It was captured in 11 

 nocturnal and 42 diurnal surface tows, 55 50-meter tows, 

 and 49 lOO-meter tows. It was often also evenly distributed 

 at all three depths at the same time. Hence the vertical dis- 

 tribution indicates indifference to weak light, with the possi- 

 bility of becoming negative as the light increases in strength. 

 All the developmental stages from nauplius to adult were 

 present in several of the surface tows. 



Macrosetella oculata (G. O. Sars) 



[Sitcllii oai/dUi G. O. Sars, Bull. Inst, oceanogr. Monaco, no. 

 323, p. 13, pi. 7, 1916.] 



This species is more tropical than gracilis and very much 

 less abundant. It was found in both oceans in 2 nocturnal 

 and 4 diurnal surface tows, 12 50-meter tows, and 17 100- 

 meter tows. The four daytime surface records were single 

 specimens, except one (/•), so that the species is negative to 

 light. The bright blue of the body and the red eyes usually 

 retain their color in formalin, making identification easy. 

 Most of the records of this species consist of single indi- 

 viduals, and no developmental stages were found. 



Genus MECYNOCERA I. C. Thompson, 1888 



Mecynocera clausi I. C. Thomp.son 



[Mccynocera clausi I. C. Thompson, Jour. Linn. Soc. London, 

 Zoo!., vol. 20, p. 150, pi. II, 188S.] 



Found everywhere in both oceans except the northern 

 regions. It was taken in 4 nocturnal and 23 diurnal surface 

 tows, 98 50-meter tows, and 90 loo-meter tows, and in the 

 vertical tow from 1000 meters, station 64. It was usually 

 present in both deeper tows at the same time, and rarely in 

 all three, hence its vertical distribution would indicate that it 

 is indifferent to weak light but negative to strong light. Its 

 small size, exceptionally long first antennae, and swollen 

 genital segment are distinguishing characters. 



Genus MEGACALANUS Wolfenden, 1904 



Megacalanus longicornis (G. O. Sars) 



[Macrocahiniis longicornis G. O. Sars, Bull. Mus. oceanogr. 

 Monaco, no. 26, p. 7, 1905.] 



This large species was well distributed in both oceans, 

 especially the tropical parts. It was present in 8 nocturnal 

 and 2 diurnal surface tows (in each of the latter a single 



specimen), 39 50-mcter tows, and 34 loo-meter tows, and in 

 the vertical tow from 1000 meters at station 64. It is, accorti- 

 ingly, negative to light, and migrates to the surface during 

 the night. The first legs are armed with a stout curved spine 

 or claw at the inner distal angle of the second basipod. 



Megacalanus princeps (Brady) 



[Calaniis princeps Brady, Voyage of H.M.S. Challenger, Zciol., 

 vol. 8, pt. 24, Copepoda, p. 36, pi. 6, figs. 3-7, 18183.) 



This species is larger than the preceding and was also 

 found in both oceans, but in much smaller numbers. It was 

 taken in i daytime surface tow, 5 50-meter tows, and 5 100- 

 meter tows, but did not appear in any of the nocturnal 

 surface tows. It was also in the vertical tow from 1000 meters 

 at station 64. Sars (1925, p. 14) has reported this copepod in 

 deep-water hauls in both oceans, and Brady (1883, p. 36) 

 found it in the Challenger plankton from the North Atlantic 

 at a depth of 1250 fathoms. 



Genus MESOCYCLOPS G. O. Sars, 1914 

 Mesocyclops leuckarti (Claus) 



[Cyclops leiic/(arti Claus, Arch. f. Naturgesch. (Berlin), vol. 23 

 (i). p. 35. pl- I. fig- 4; pl- 2, figs. 13, 14, 1S57.] 



A few specimens of this well known species were found 

 in a lagoon or pond on Penrhyn Island in the tropical 

 Pacific. The water must have been at least brackish if not 

 saline, since the other nine species taken at this locality were 

 all typical marine forms. 



Genus METIS Philippi. 1843 



Metis jousseaumei (Richard) 



[llyopsylliis joiissciiumci Richard, liull. Soc. zool. France, vol. 

 17, p. 69, 1892.] 



Two females of this minute harpactid were present in a 

 surface tow taken at the ship's anchorage at Hanga Roa, 

 Easter Island. The anchorage must have been in an open 

 roadstead, since this was the only species to give an idea of 

 the proximity of land, and all the other species were pelagic 

 forms. 



Genus METRIDIA Boeck, 1865 



Metridia brevicauda Giesbrecht 



\Metriilia brcmcauda Giesbrecht, Atti R. Accad. Lincei, Rome, 

 ser. 4, vol. 5, sem. 2, p. 24, 1889; Fauna und Flora des Golfes 

 von Neapel, vol. 19, pp. 340, 346, pl. 33, figs. 5, 10, 11, 14, 

 21, 26, 32, 1892.] 



Not found in the Atlantic plankton, and in the Pacific 

 practically confined to a few localities in the southeastern 

 region. It was taken in i nocturnal surface tow, 2 50-meter 

 tows, and 6 loo-meter tows. These few specimens were 

 negative to light but showed occasional migration to the 

 surface at night. All the specimens (22) in the Siboga 

 plankton were captured in vertical hauls from depths of 750 

 to 1500 meters. The species has been reported from the 

 South Atlantic by Cleve (1904, p. 192). 



