DISCUSSION OF SPECIES 



207 



Siboga plankton, and most of the specimens were taken at 

 the surface either at night or in the daytime. 



Genus SCAPHOCALANUS G. O. Sars, 1900 



Scaphocalanus elongatus A. Scott 

 (Figure 113) 



[ScaphocLihviiiS elongatus A. Scott, Copepoda of Siboga Exped., 

 vol. 29rt, pt. I, p. 98, pi. 32, figs. 10-16, 1909.] 



A single female was obtained in the loo-meter tow at 

 station 107 in the western tropical Pacific, and this was the 

 only record for the cruise. The specimen which A. Scott 

 (1909, p. 98) described under the above name was taken not 

 far from the same locality. Since the Siboga and Carnegie 

 planktons each yielded but a single specimen, the species 

 must be quite rare. 



Scaphocalanus magnus (T. Scott) 



[Aniallop/iora magna T. Scott, Trans. Linn. Soc. London, ser. 

 2, Zool., vol. 6, pt. I, p. 55, pi. 6. figs. 5-9, 1894.] 



A single female was obtained in the vertical tow from a 

 depth of 1000 meters at station 64 in the southeastern Pacific. 

 It is easily distinguished by the helmet-shaped crest on the 

 forehead and the structure of the fifth legs. Half the speci- 

 mens obtained in the Siboga plankton were found in vertical 

 tows from considerable depths, and the other half in surface 

 tows at night. It thus seems probable that this is a deep- 

 water species remaining below 100 meters in the daytime. 



Scaphocalanus medius (G. O. Sars) 

 (Figure 136) 



[Amallophora media G. O. Sars, Bull. Inst, oceanngr. Monaco. 

 no. loi, p. 16, 1907.] 



A single female was taken in the 100-meter tow at station 

 56 in the southeastern Pacific. This is another deep-water 

 species, and has been found in both oceans, but probably 

 remains below 100 meters most of the time. It has no crest, 

 and the structure of the fifth legs is quite different from that 

 in the other two species of the genus. 



Genus SCOLECITHRICELLA G. O. Sars, 1902 



This genus is distinguished from Scolccithrix by the 

 presence of a fifth pair of legs in the female as well as the 

 male. 



Chart 16. Daytime vertical distribution of certain species of 

 Scolecithricella: (i) abyssalis, (2) auropecten, (3) bradyi, (4) 

 maiginata, (5) minor. 



Scolecithricella abyssalis (Giesbrecht) 

 (Figures 120, 132) 



[Scolccithrix abyssalis Giesbrecht, Atti R. .A.ccad. Lincei, Rome, 

 ser. 4, vol. 4, sem. 2, p. 338, 1888; Fauna und Flora des 

 Goifes von Neapel, vol. 19, pp. 266, 284, pi. 13, figs. 15, 40; 

 pi. 37, fig. 7, 1892.] 



Not found in the Atlantic plankton, and in the Pacific 

 virtually confined to the eastern and central tropical regions. 

 It was taken in 3 50-meter tows and 7 loo-meter tows, but in 

 none of the surface tows either by day or by night. This 

 makes the species negative to light and furnishes no evi- 

 dence with regard to nocturnal migration. As in the Siboga 

 plankton, all the specimens found were females and the male 

 is still unknown. The species has been reported from the 

 Faroe Channel in the North Atlantic. 



Scolecithricella auropecten (Giesbrecht) 

 (Figure 121) 



[Scolccithrix auropecten Giesbrecht, Fauna und Flora des Goifes 

 von Neapei, vol. ig, pp. 266, 284, pi. 13, figs. 8, 18, 22, 27; 

 pi. 37. figs. 3, 10, 1892.] 



Not found in the Atlantic plankton, and in the Pacific 

 segregated in the southeastern and central regions. It was 

 taken in i 50-meter tow and 5 lOO-meter tows, and in the 

 vertical tow from 1000 meters, station 64, but did not appear 

 at all at the surface. As in the case of abyssalis, this makes 

 the species negative to light and gives no evidence of noc- 

 turnal migration. The long aesthetasks on the first antennae 

 were very noticeable and looked like strings tied to a wire. 

 The 2 specimens in the Siboga plankton were taken in ver- 

 tical hauls from depths of 900 and 1000 meters. 



Scolecithricella bradyi (Giesbrecht) 



[Scolccithrix bradyi Giesbrecht, Atti R. .'\ccad. Lincei, Rome, 

 ser. 4, vol. 4, sem. 2, p. 337, 1888; Fauna und Flora des 

 Goifes von Neapei, voi. 19, pp. 266, 283, pi. 4, fig. 7; pi. 13, 

 figs. I, 3, 7> ".. ^h ^S; pi. 37, figs. I, 2, 9, 1892.] 



Not present in the Atlantic plankton, but well distributed 

 in the Pacific, especially the southeastern and western regions. 

 It was taken in 8 nocturnal and 2 diurnal surface tows, 18 

 50-meter tows, and 18 loo-metcr tows, and at station 64 in 

 the vertical tow from 1000 meters. This record gives good 

 evidence of nocturnal migration to the surface and a return 

 to the deeper layers in the daytime. The fifth legs of the 

 female are so small as to be easily overlooked unless care- 

 fully searched for, but in the male they are fairly large and 

 prehensile. In the Siboga plankton 5 specimens were taken 

 in vertical hauls from depths of 750 to 1500 meters, and i at 

 the surface at night. 



Scolecithricella marginata (Giesbrecht) 



(Figures 122, 133) 



[Scolccithrix marginata Giesbrecht, Atti R. Accad. Lincei, 

 Rome, .ser. 4, voi. 4, sem. 2, p. 33S, 1888; Fauna und Flora 

 des Goifes von Neapei, voi. 19, pp. 266, 285, pi. 13, figs. 10, 

 31, 1S92.I 



Not found in the ,\tlantic plankton, but at a few localities 



