584 BULLETIN 159, UNITED STATES NATIONAL MUSEUM 



9. Urosome 3-segmented; genital segment spindle-shaped, its pos- 



terior margin no wider than the abdomen, with no trace of 

 sixth legs at the corners; sponge washings (Ceylon). 



9 Asteropontius Thompson and Scott, 1903 

 Urosome 4-segmented; genital segment quadrangular, its pos- 

 terior margin twice as wide as abdomen, with rudimentary 

 sixth legs at the corners; parasitic on starfish. 



cT Scottomyzon Giesbrecht, 1897 



10. Sucking tube reaching fifth metasome segment; caudal rami 



half as long as anal segment; end segment of fifth leg lamelli- 

 form, with 3 apical setae; dredged, 20 fathoms. 



cf ? Scottocheres Giesbrecht, 1897 

 Sucking tube not reaching first legs except in one species of 



Asterocheres; caudal rami as long as anal segment, or longer 11 



11. Caudal setae much shorter than urosome; end segment of fifth 



leg not tapered distally and ciliated only on its inner margin; 



parasitic on echinids 9 Echinocheres Claus, 1889 



Caudal setae much longer than urosome; end segment of fifth 

 leg considerably tapered distally and ciliated on both mar- 

 gins; parasitic on starfish cf 9 Asterocheres Boeck, 1859 



12. Endopod of fourth leg reduced in size, with minute setae; head 



and metasome segments with pointed epimeral plates; end 

 segment of fifth leg tiny; pelagic, varying depths. 



cf 9 Bradypontius Giesbrecht, 1895 

 Endopod of fourth leg not reduced, with setae of normal size; 



head and most of metasome segments without epimeral plates 13 



13. Oral cone pear-shaped, not produced into a sucking tube; endo- 



pod of second antenna with an apical spine and 1 or 2 setae 14 



Oral cone ovoid and produced into a sucking tube; endopod of 



second antenna with 3 or more apical plumose setae 17 



14. Rostrum, large, pointed, beak-shaped; third and often the 



second metasome segments with pointed posterior corners; 

 caudal rami long and slender; dredged, moderate depths. 



c? 9 Rhynchomyzon Giesbrecht, 1895 

 Rostrum small, blunt; second and third segments with rounded 



corners 15 



15. Caudal rami and end segment of fifth leg little longer than wide; 



the latter with 2 setae, 2 spines, and a bristle; urosome 

 segments pointed; dredged, moderate depths. 



cf 9 Dermatomyzon Claus, 1889 

 Caudal rami four to ten, end segment of fifth leg three to eight 



times as long as wide; urosome segments rounded 16 



16. Oral cone truncated, with 2 diverging apical tentacles; caudal 



rami four, end segment of fifth leg three times as long as 

 wide, with 3 apical setae; dredged, moderate depths. 



9 Leptomyzon G. O. Sars, 1915 

 Oral cone bluntly rounded, without tentacles; caudal rami ten, 

 end segment of fifth leg in female eight, in male four, times as 

 long as wide; dredged, 30 fathoms cf 9 CoUocheres Canu, 1893 



