DISCUSSION OF SPECIES 



199 



in the distribution, one of them including all the stations 

 from 69 to 106 inclusive. It was present in 15 nocturnal and 

 1 1 diurnal surface tows, 16 50-meter tows, and 19 100-meter 

 tows, and in the vertical tow from 1000 meters at station 64. 

 The preference for the two deeper tows in the daytime was 

 only slight, and the species would seem to be somewhat in- 

 ilifferent to light. The species was reported by CJiesbrecht 

 (i8gi, p. 477; 1892, p. 591) from the tropical Pacific down 

 to 1000 meters, and by Sars (1900, p. 107) from the Arctic 

 Ocean north of the New Siberian Islands. 



Oncaea ornata Giesbrecht 



(Figure 48) 



\Oncaea ornata Giesbrecht, Atti R. Accad. Lincei, Rome, ser. 4, 

 vol. 7, sem. I, p. 477, 1891; Fauna und Flora des Golfcs von 

 Neapei, vol. 19, pp. 591, 604, pi. 44, figs. 50, 51; pi. 47, figs. 

 20, 24, 49, 53, 1892.] 



Five females were obtained in a surface tow off Samoa 

 Island at night, and this was the only record for the cruise. 

 The species was originally reported by Giesbrecht (1891, 

 p. 477; 1892, p. 591) from the eastern tropical Pacific, and 

 has not been noted in the plankton of any expedition since 

 then. It is thus very rare, and is probably much restricted in 

 distribution. 



Oncaea similis G. O. Sars 



[Oncdca si nulls G. O. Sars, Crustacea of Norway, vol. 6, p. 

 193, pi. 109, fig. I, 1918.] 



Found at three localities in the Atlantic and well distrib- 

 uted in the southeastern and eastern Pacific, but extremely 

 scattering elsewhere. It was present in 16 nocturnal and 9 

 diurnal surface tows, 30 50-meter tows, and 24 loo-meter 

 tows, and in the vertical tow from 1000 meters, station 64. It 

 thus showed a definite choice of the deeper tows in the day- 

 time and a habitual resort to the surface at night. This is 

 the first record of this species from the Pacific Ocean. 



Oncaea subtilis Giesbrecht 



[OiiCiUa subtilis Giesbrecht, Fauna und Flora des Golfes von 

 Neapei, vol. 19. pp. 591, 603, pi. 47, figs. 14, 18, 25, 43, 60, 

 1892.] 



Found at only two of the Caribbean Sea stations and 

 almost entirely at the eastern tropical stations in the Pacific. 

 It was taken in 4 nocturnal and 4 diurnal surface tows, 8 

 50-meter tows, and 6 loo-meter tows. Not enough specimens 

 were obtained to warrant any general conclusions, but it 

 seems fairly evenly distributed among the three depths and 

 hence might be considered as probably indifferent to light. 



Oncaea tenella G. O. Sars 



[Onaica tcnclla G. O. Sars. Bull. Inst, oceanogr. Monaco, no. 

 ill, p. 12, pi. 5, 1916.I 



Found at two Caribbean and three mid-tropical Atlantic 

 stations, but chiefly in the southeastern Pacific. It was 

 present in 12 nocturnal and 9 diurnal surlace tows, 14 50- 

 meter tows, and 18 100-meter tows, and in the vertical tow 

 from 1000 meters at station 64. It showed, therefore, a 



moderate preference for the deeper tows by day and migra- 

 tion to the surface at night. This is another of Sars' (1916, 

 p. 12) species, and was originally obtained from the Mediter- 

 ranean. 



Oncaea venusta Philippi 



[Oncaea venusta Philippi, Arch. f. Naturgesch. (Wiegmann), 

 vol. I, Jahrg. 9, p. 63, fig. 3. 1843.I 



This shares with miniita the widest distribution and the 

 greatest abundance of any species of the genus. Indeed, they 

 are surpassed in these respects only by Oithona similis among 

 all the copepods of the Carnegie plankton. This species was 

 captured in 31 nocturnal' and 80 diurnal surface tows, 103 

 50-meter tows, and 102 loo-meter tows, and in the vertical 

 tow from 1000 meters at station 64. It was recorded one hun- 

 dred and fifty-four times as abundant and one hundred 

 times as common. It was found more often than any other 

 copepod distributed equally at all three depths at the same 

 time. It is therefore indifferent to light, and its vertical dis- 

 tribution is exceptionally uniform. 



Genus ONCHOCALANUS G. O. Sars, 1905 



Onchocalanus cristatus (Wolfenden) 

 (Figure 90) 



[Xanthocahvuis cristatus Wolfenden, Jour. Marine Biol. Assoc, 

 n. s., vol. 7, no. i. p. 119, pi. 9, figs. iS, 19, 1904.] 



A single female was taken in the vertical tow from a depth 

 of 1000 meters at station 64 in the southeastern Pacific, and 

 this was the only record for the entire cruise. This species 

 occurred twice in the Siboga plankton in vertical hauls from 

 depths of 1000 and 1536 meters respectively. It is probably, 

 therefore, a deep-water species which stays below the 100- 

 meter level at least in the davtime. 



Onchocalanus niidipes, new species 

 (Figures 71-83) 



Occurrence. About 40 specimens in various stages of de- 

 velopment were taken in the eastern, central, and western 

 parts of the tropical Pacific, but none were found in the 

 Atlantic plankton. They were captured in 6 surface tows, 2 

 50-meter tows, and 3 100-meter tows. No adult males were 

 obtained, although some of the younger stages were prob- 

 ably undeveloped males. 



Description of female. Body pyriform, the metasome con- 

 siderably widened and much inflated dorsally and ventrally, 

 the urosome one-fourth as long and one-fifth as wide as the 

 metasome and four-segmented. The head is separated from 

 the first segment, and the fourth from the fifth segment. The 

 genital segment is half the length of the urosome and a little 

 wider than the abdomen. The three abdominal segments are 

 equal in length and width, but the anal segment is shortened 

 at the sides. The caudal rami are as wide as long, divergent, 

 and each is armed with four setae of about equal length. 



The first antennae are slender and twenty-four-segmented, 

 and reach the middle of the urosome. The exopod of the 

 second antenna is twice as long as the endopod and six- 

 segmented, the second segment twice as long as the first. 



