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274 PROCEEDINGS OF THE NATIONAL MUSEUM 



Farran also shows shorter terminal setae on P5 in the Christmas 

 Island specimens, perhaps because the distal parts of these setae are 

 very delicate and difficult to see. 



Oithona alia (Kiefer, 1935), from India, resembles 0. oculata but 

 differs in lacking ocular lenses and in having the inner terminal seta 

 of P5 much shorter than the outer seta. Other differences given by 

 Kiefer are of doubtful significance. 



Distribution.— Christmas Island, Indian Ocean (Farran) ; Samoa 

 (Rosendorn) ; Nicobar Island (Sewell) ; Cape of Good Hope (Tanaka) ; 

 Ifaluk AtoU, Caroline Islands (Vervoort) ; coast of Brazil (Bjornberg). 

 Our Puerto Rican specunens constitute the 2nd Atlantic record for 

 this species. We have also identified specimens from Lameshur Bay, 

 St. John, Virgin Islands. 



Oithona simplex Farran 



Figures 2lf-i 



Oithona simplex Farran, 1913, pp. 187-188, pi. 29, figs. 10-14; pi. 30, figs. 1, 2.- 



Rosendorn, 1917, pp. 44-46.— Gurney, 1927, p. 160.— Kiefer, 1929, p. 9.— 



Grice, 1960a, pp. 222-223; 1960b, p. 488, figs. 12-18.— Tanaka, 1960, pp. 



64-65, pi. 28, figs. 1-6. 



Female.— Length 0.36-0.43 nam. Prosome:urosome = about 2.0. 



Prosome rather heavyset in dorsal view; head broadly rounded 



anteriorly; rostrum absent. Anal segment about twice as wide as 



long; caudal ramus rather short, about 1.5 times as long as wide, 



lateral marginal seta inserted near proximal end, nearly as long as 



ramus. Lateral apical seta about twice as long as ramus. Relative 



lengths of apical setae (lateral apical seta = 1) : 1:2:3:1.3. Al reaches 



to or slightly beyond posterior margin of PedSeg 1 . B2 of Md bearmg 



a long stiff seta armed with a few large setules and a slender finely 



plumose seta; Ri with 5 setae. Ri of PI 2-segmented. Re of P1-P4 



armed as foUows: 



Outer setae: 1-1-3, 1-1-3, 1-1-3, 1-1-3. 

 Inner setae: 1-1-4, 1-1-5, 1-1-5, 1-1-5. 

 P5 with single terminal seta. 



Male.— Length about that of female. Prosome :urosome = about 

 1.4. Anal segment very short, as in female. Al typicaUy folded in 



U -shape. i -d 4. 



Remarks.— 0. simjylex can be distinguished from the other Puerto 

 Rican species of Oithona by its small size, plump prosome, short 

 urosome, short anal segment, the setae on B2 of the Md, and the 

 2-segmented Ri of Pi. As Grice (1960b) has pomted out, it differs 

 in several respects form Farran's description. The prosome: urosome 

 ratio is greater; Al is shorter; the smaU inner seta of Rel and the 



