600 BULLETIN 159, UNITED STATES NATIONAL MUSEUM 



16. Males, urosome not segmented; first antennae 7-segmented; 



second antennae 4-segmented and nonprehensile; fifth legs 



wholly lacking; on mollusks cf Enteropsis Aurivillius, 1885 



Females, urosome 4-segmented; eggs carried in external ovisacs 17 



17. Metasome distinctly segmented; caudal rami slightly divergent, 



with apical setae; fifth legs laminate, covering the ovisacs; 



in ascidians 9 Ascidicola Thorell, 1859 



Head separated, rest of metasome fused; caudal rami turned 

 outward, with claws; fifth legs conical, not covering ovisacs; 

 in ascidians 9 Botryllophilus Hesse, 1864 (p. 392) 



18. Second antennae 3-segmented, armed with claws or setae 19 



Second antennae 2-segmented, armed with spines or claws 23 



Second antennae 1-segmented and unarmed 28 



19. A single spherical ovisac on dorsal surface of urosome; fifth legs 



conical, widely separated and not covering ovisac; in ascidians. 



9 Botryllophilus Hesse, 1864 (p. 392) 

 A single flattened ovisac on dorsal surface of urosome, covered 



at its base by the partially fused laminate fifth legs 20 



Two external ovisacs attached to sides of genital segment; fifth 



legs entirely separate on sides of fifth segment 21 



Two external ovisacs ; fifth legs entirely lacking 22 



20. Urosome 5-segmented; caudal rami obliquely divergent; first 



antennae 4-segmented; leg endopods laminate, with apical 



and outer spines; in ascidians cf 9 Schizoproctus Aurivillius, 1885 



Urosome 3-segmented; caudal rami at right angles to body axis, 

 first antennae 6-segmented; leg endopods conical, with long 

 apical setae; in ascidians 9 Pteropygus G. O. Sars. 1921 



21. Fifth legs conical lobes, widely separated; ovisacs cylindrical, 



longer than body; end segment of second antenna minutely 



denticulate; in ascidians 9 Cryptopodus Hesse, 1865 



Fifth legs curved lamellae, meeting dorsally; ovisacs club- 

 shaped, shorter than body; end segment of second antennae 

 setose; in ascidians 9 Enterocola Beneden, 1860 



22. Mandibles 1-segmented processes of medium size, with 3 setae; 



first maxillae biramose and well developed, with several 



setae; in ascidians 9 Haplostomides Chatton and Harant, 1924 



Mandibles mere knobs, each with 1 or 2 setae; first maxillae 

 lacking; exopods of swimming legs with terminal and several 

 outer claws; in ascidians 9 Haplostoma Canu, 1886 



Mandibles and maxiUae both lacking; exopods of swimming 

 legs each with one terminal claw only; no caudal rami; in 

 ascidians 9 Haplosaccus Chatton and Harant, 1924 



23. Fifth legs present and biramose like the other pairs; first an- 



tennae 1-segmented; urosome with lateral wings; eggs in 2 



ovisacs; in ascidians 9 Hypnoticus Wilson, 1924 



Fifth legs present, uniramose and 1-segmented 24 



Fifth legs replaced by folds of skin; first antennae laminate, 

 1-segmented, unarmed; urosome without wings; eggs in 2 



ovisacs; in ascidians 9 Ophioseides Hesse, 1864 



Fifth legs entirely lacking 27 



