DISCUSSION OF SPECIES 



183 



width. Each of the segments of the urosome carries at each 

 posterior corner a fingeHike process which curves inward and 

 overlaps the segment next behind it. Each caudal ramus is as 

 long as the anal segment and two-thirds as wide as long, with 

 four posterior setae and one on the dorsal surface which is 

 attached to an enlarged and projecting base. 



The head has a small knob at the center of the anterior 

 margin, on a level with the dorsal surface, but no actual 

 rostrum. The first antennae are eight-segmented, the basal 

 segment the shortest, the terminal segment the longest. The 

 second, third, and eighth segments carry numerous setae, and 

 the sixth segment has a slender aesthetask which reaches 

 beyond the tip of the antenna. The second antenna is uni- 

 ramose and four-segmented, the end segment with four setae 

 of which the terminal one is the longest. 



The mouth tube is short and curved backward, and stands 

 out nearly at right angles to the ventral surface of the head; 

 it is slightly enlarged at the tip, with a radiating flange. The 

 mandibular palp is setaceous, consisting of a narrow cylin- 

 drical joint carrying at its tip a long seta. The first maxilla 

 has the inner lobe well developed and tipped with two stout 

 setae, the outer lobe slightly longer with three setae. The 

 second maxilla and maxilliped are unguiculate; the dactylus 

 of the former is distinctly two-jointed, the terminal part 

 strongly curved and armed on its outer surface at the proxi- 

 mal end with two rows of denticles which join distally and 

 at the point of junction carry a fingerlike process. The dac- 

 tylus of the maxilliped is triarticulate, the terminal part 

 lightly curved and with a single row of cilia on the ventral 

 surface. 



The first four pairs of legs have three-segmented rami with 

 the spines and setae arranged as follows: first exopod i-o, 

 i-i, 2-5, endopod i-i, 0-2, 0-7; second exopod i-i, i-i, 3-4, 

 endopod i-i, 0-2, 0-6; third exopod o-i, i-i, 3-3, endopod 

 I-I, 0-2, 0-5; fourth exopod o-i, i-i, 2-3, endopod i-i, 0-2, 

 0-4. The fifth legs are entirely lacking, but each is replaced 

 by a small seta just inside the posterior corner of the fifth 

 segment. 



Total length, 1.35 (i. 25-1.45) mm; length of metasome, 

 0.80 mm; width, 0.65 mm; length of urosome, 0.55 mm; 

 width, 0.15 mm. 



Type. U. S. Nat. Mus. no. 64003. 



Remavl{.(. This is evidently a surface copepod, but it occa- 

 sionally retires to the 50-meter or even the 100-meter level. 

 The suctorial character of the mouth is suited to a more or 

 less parasitic existence, but all the present specimens were 

 taken while free-swimming and there is nothing to indicate 

 the character or identity of a possible host. 



Genus DREPANOPUS Brady, 1883 

 Drepanopus pectinatus Brady 



[Drepanopiis pcctincttiis Brady, Voyage of H.M.S. Challenger, 

 Zool., vol. S, pt. 23, Copepoda, p. 77, pi. 24, figs, i-ii, 1883.] 



A few specimens, including both sexes, were obtained in 

 the loo-metcr tow at station 4 in the northern central 

 Atlantic, and this was the only record for the entire cruise. 



Brady's (1883, p. 77) original specimens were taken at Ker- 

 guelen Island in the southern Indian Ocean and in the open 

 sea west of it. Giesbrecht (1892, p. 201) reported another 

 species from the South Atlantic and the South Pacific. As far 

 as is known, this is the first record of any species of the genus 

 from the North Atlantic. The species is evidently very rare 

 and is confined to isolated localities. 



Genus DYSGAMUS Steenstrup and Liitken, 1861 



Dysgamus atlanticus Steenstrup and Liitken 



(Figure 32) 



[Dysgaimis atlauticus Steenstrup and Liitken, Kong. Danske 

 V'idensk. Selsk. Skr., ser. 5, Naturliist. og. matli. Afd., vol. 5, 

 p. 368, pi. 4, fig. 8, 1861.I 



A single male was found in the lOo-meter tow at station 

 156 in the central tropical Pacific, in latitude 3° north. In 

 addition to the original description of the species by Steen- 

 strup and Liitken (1861, p. 368), Lonnberg (1889, p. 150) 

 published a more detailed and accurate account. But neither 

 of these papers contained a figure showing the pattern of the 

 dorsal surface of the metasome, which is of considerable 

 assistance in identifying the species. Since the Carnegie speci- 

 men showed this pattern rather distinctly, a figure of it is 

 here introduced (fig. 32) for comparison with those of the 

 other two species of the genus already published by the pres- 

 ent author (D. ayiommus Wilson, 1907, p. 713, pi. 20, figs. 

 62-70; D. longij meatus Wilson, 1923, p. 11, pi. 2, figs. 20- 



Genus EUAETIDEUS G. O. Sars, 1925 

 Euaetideus bradyi (A. Scott) 



[Actidetts bradyi A. Scott, Copepoda of the Siboga Exped., vol. 

 2917, pt. I, p. 38, pi. 5, figs. 1-12, 1909.] 



Four specimens of this species were found in the eastern 

 Pacific, I in a nocturnal surface tow, the other 3 in 100- 

 meter tows. These 3 were negative to light, but the i shows 

 that it comes to the surface during the night. It is worthy 

 of note that all the 25 specimens recorded as obtained in the 

 Siboga plankton were taken in vertical tows from various 

 depths, the minimum being 700 meters. This suggests that 

 the species is a deep-water form that would not be found 

 very often within the upper lOO meters during the daytime. 



Euaetideus giesbrechti (Cleve) 



[Actidcus giesbrechti Cleve, Marine Invest. South Africa, vol. 3, 

 pt. I, Copepoda, p. 185, 1904.] 



Not found in the Atlantic plankton, and in the Pacific 

 found chiefly in the eastern and southeastern regions. It was 

 taken in i 50-meter tow and 9 100-meter tows, but nowhere 

 at the surface either by day or by night. All the specimens 

 cff this species in the Siboga plankton were taken in vertical 

 tows from considerable depths, with one exception, 5 speci- 

 mens taken at the surface at night. It is thus strongly nega- 

 tive to light but does come to the surface during the night. 



