DISCUSSION OF SPECIES 



195 



Genus MONSTRILLA Dana, 1849 



Monstrilla inserta A. Scott 



[Monstnllii inscita A. Scott, Copepoda of the Siboga Exped., 

 vol. 2()a, pt. I, p. 237, pi. 57, figs. 7, 8, 1909.] 



This species was not present in the Atlantic plankton and 

 was taken at two stations (109 and 112) only in the Pacific, 

 in the 50-meter tows. The short first antennae and the struc- 

 ture of the fifth legs are distinctive characters. All the Siboga 

 specimens were taken at the surface, once at night and twice 

 in the daytime, but the Carnegie specimens had migrated 

 downward to the 50-meter level. 



Genus NEOCALANUS G. O. Sars, 1925 



Neocalanus gracilis (Dana) 

 (Figure 84) 



\Ciihiniis gracilis Dana, Proc. Amer. Acad. Arts and Sci., vol. 

 2, p. 18, 1849; U. S. Exploring Exped., 1838-1842 (Wilkes), 

 vol. 14, pt. 2, Crustacea, p. 1078, 1853; pi. 74, fig. 10, 1855.] 



Found at four Atlantic stations and well distributed 

 throughout the entire Pacific. It was taken in 17 nocturnal 

 and 18 diurnal surface tows, 72 50-meter tows, and 78 100- 

 meter tows, as well as at station 64 in the vertical tow from 

 1000 meters. It therefore migrates to the surface at night 

 and is probably negative to strong light. The exceptionally 

 long antennae and the peculiarly barbed terminal spine on 

 the exopod of the first legs identify the species. Sars (1925, 

 p. 7) reported this species from 112 stations of the various 

 Monaco expeditions, the majority of the species from depths 

 greater than 100 meters. 



Neocalanus robustior (Giesbrecht) 



[Ciiliiiuis robustior Giesbrecht, Atti R. Accad. Lincei, Rome, 

 ser. 4, vol. 4, seni. 2, p. 332, 1888; Fauna unci Flora des 

 Golfes von Neapel, vol. ig, pp. 91, 129, pi. 7, figs. 19, 25, 30; 

 pl. 8, fig. 34, 1892.] 



Not present in the Atlantic plankton, but well distributed 

 in the Pacific. It was found in 13 nocturnal and i diurnal 

 surface tow, 49 50-meter tows, and 51 loo-meter tows, and 

 in the vertical tow from 1000 meters, station 64. It is more 

 negative to light than the preceding species, and migrates to 

 the surface at night. The shorter and stouter first antennae 

 and the left fifth foot of the male characterize the species. 

 This species was reported by Sars (1925, p. 8) from only 

 ten of the Monaco stations, and is evidently not so widely 

 distributed as gracilis. 



Neocalanus tenuicornis (Dana) 



[Ctihiiitis tenuicornis Dana, Proc. Amer. Acad. Arts and Sci., 

 vol. 2, p. 15, 1849; U. S. Exploring Exped., 1838-1842 

 (Wilkes), vol. 14, pt. 2, Crustacea, p. 1069, 1853; pl. 73, fig. 

 loa, b, 1S55.] 



Found at four Atlantic stations and sparingly distributed 

 in the Pacific except in the southeastern part. It was present 

 in 8 nocturnal and 4 diurnal surface tows, 32 50-meter tows, 

 and 52 100-meter tows. The exceptionally long and filiform 



first antennae serve to distinguish the species, which is less 

 widely distributed than robust/or. 



Genus NESIPPUS Heller, 1865 



Nesippus species 



(Figure 31) 



One male Nesippus was taken at the surface in the western 

 Pacific, station 106, the only record for the cruise. It re- 

 sembled Dana's Specilligus curticaudis (1849, p. 58; 1853, 

 P- '375> pl- 95' fig- (>a-k), but differed in many particulars, 

 especially the frontal plates, the anterior and posterior mar- 

 gins of the carapace, and the abdomen. It was impossible to 

 decide from the single specimen whether it was to be re- 

 garded as a variety or a separate species. A drawing is here 

 included for comparison with other species of the genus and 

 as an aid in future identification (fig. 31). 



Genus OITHONA Baird, 1843 



This genus of cyclopoid copepod is characterized by the 

 small size of the species and by the slender and elongated 

 urosome. The present records show that all the species fre- 

 quent the two deeper tows in preference to the surface. In 

 geographical distribution, however, the genus as a whole 

 shows but little partiality for any region or zone, since most 

 stations in both oceans yielded from one to five species. The 

 average number of species for each station for the entire 

 cruise was three, but the number was somewhat larger in 

 the southeastern and central Pacific and considerably smaller 

 in the northern regions of both oceans. 



Ch.\rt 12. Daytime vertical distribution of species of Oithona: 

 (i) attenuata, (2) hrevicornis, (3) jallax, (4) hcbes, (5) linearis, 

 (6) plumijera, (7) robtista, (8) setiger, (g) similis, (10) spini- 

 rostris, (11) vivida. Three species appeared only in the lOO-meter 

 tow; one was found at the surface and in the loo-meter tow, but 

 not in the 50-meter tow; one was confined to the two deeper tows. 

 The other six species were present at all three depths and were 

 least abundant at the surface. Three of them were most abundant 

 in the 50-meter tow and the other three in the 100-meter tow. 

 The two species similis and spinirostris were by far the most 

 numerous, and the former was the one that appeared most often 

 in the nocturnal surface tows. 



