228 



BULLETIN 15 8, UNITED STATES NATIONAL MUSEUM 



distal segment, with five setae, the middle one longest; distal seg- 

 ment about as wide as long, with five setae, the second inner one 

 longest. Total length, 0.74 mm. 



Male. — Body shorter than that of female, relatively as wide. First 

 antennae not geniculate, fourth segment as long as first, second a 



little shorter, third only half 



\ 



FiGUKB 153. — Aniphiascus oommensalis : a. 

 Female, dorsal (after Seiwell) ; ft, female, 

 fifth leg ; c, male, fifth leg 



the length. Both rami of first 

 leg 3-segmented, the endopod a 

 little longer than the exopod; 

 endopod of second leg also 

 longer than exopod, its end seg- 

 ment transformed into a stout 

 spine. Fifth legs smaller than 

 in the female, the inner expan- 

 sion of the basal segment with 

 but two setae. Total length, 

 0.65 mm. 



Remarks. — Most of the species 

 of this genus hitherto described 

 have been taken from among 

 algae and hydroids or close to 

 the bottom mud. We can under- 

 stand, therefore, how the pres- 

 ent species has become com- 

 mensal wdthin an ascidian. As 



it is the only one with such a habitat, that fact alone is sufficient 



to distinguish it. 



Genus STENHELIA Boeck, 1864 



Body more or less pyriform; head fused with the first segment 

 and much swollen; rostrum rigid, broadly triangular, and indented 

 on either side near the tip; urosome short and usually tapered pos- 

 teriorly ; genital segment more or less divided ; caudal rami longer 

 than wide. First antennae 8-segmented, geniculate in the male; 

 exopod of second antennae 3-segmented, the middle segment very 

 short; mandibular palp biramose; maxillipeds unguiculate; rami of 

 first four pairs of legs 3-segmented, except the first endopod, which 

 is sometimes 2-segmented; fifth legs 2-segmented, the distal segment 

 extended laterally and visible in dorsal view; two ovisacs, more or 

 less divergent. 



KEY TO THE SPECIES (FEMALES) 



1. Distal segment of fifth leg as wide as long, with 6' setae, basal 



expansion with 4 setae arenicola, new species (p. 229) 



Distal segment of fifth leg longer tliiin wide, with 5 setae, basal 



expansion with 5 setae . reflexa (p. 230) 



