350 BULLETIN 15 8, UNITED STATES NATIONAL MUSEUM 



Apparently this species never becomes parasitic, but always remains 

 free swimming. 



Family ONCAEIDAE 

 Genus ONCAEA Philippi, 1843 



Body cyclopoid; metasome elongate, elliptical, strongly vaulted 

 dorsally; head separated from first segment and about half the 

 length of the metasome. Urosome 4-segmented in female, 5-seg- 

 mented in male; genital segment considerably enlarged, especially 

 in male; caudal rami shorter than anal segment. First antennae 

 6-segmented; second antennae 3-segmented, nonprehensile ; rami of 

 first four pairs of legs 3-segmented, end segments elongated, exopods 

 with coarse daggerlike spines; fifth legs minute, each 1-segmented, 

 with two subequal apical setae. 



KEJY TO THE SPECIES 

 FEMALES 



1. Second thoracic segment raised into a prominent hump on dor- 



sal midline 2 



Second thoracic segment smooth dorsally, no hump 3 



2. Genital segment from one-half longer to twice as long as abdo- 



men ; inner apical seta of fifth leg twice as long as outer 



one conifera (p. 350) 



Genital segment scarcely longer than abdomen ; the 2 apical 



setae of fifth leg subequal in length borealis (p. 351 ) 



3. Cephalic segment as long as rest of metasome, widest at its 



posterior margin ; metasome elliptical minuta (p. 352) 



Cephalic segment one-half shorter than rest of metasome, widest 



at its center; metasome obovate venusta (p. 353) 



MALES 



1. Genital segment four times length of abdomen; caudal rami 



longer than anal segment venusta (p. 353) 



Genital segment relatively much shorter; caudal rami shorter 



than anal segment 2 



2. Genital segment twice as wide as abdomen, with straight sides 



and sharply pointed posterior comers conifera (p. 350) 



Genital segment three times as wide as abdomen, with strongly 



convex sides and bluntly rounded posterior corners ^ borealis (p. 351) 



ONCAEA CONIFERA Giesbrecht 

 FlGUBE 210 



Oncaea conifera Giesbbecht, Fauna und Flora des Golfes von Neapel, vol. 19, 

 p. 591, pi. 2, 47, 1892. 



Occurrence. — Both sexes were taken in a surface tow at Station 

 20107, Grampus., off Georges Bank. 



Distribution. — Arctic Ocean (Willey, Mrazek) ; Mediterranean 

 (Claus) ; tropical Pacific (Giesbrecht) ; Red Sea, Indian Ocean 



