490 PROCEEDINGS OF THE NATIONAL MUSEUM vol.99 



to major subdivisions. The form of the proboscis is perhaps equally 

 valid, but this organ is obviously more susceptible to environmental 

 influences and it is unfortunately sometimes missing. As a working 

 hypothesis I have assumed that basal nephrostomes are the most prim- 

 itive; that two nephridia are more ancestral than one, for the same 

 reason that an undivided proboscis is more ancestral; and that the 

 occurrence of two setae, with typical echiuroidean muscle apparatus, 

 precedes in evolution a condition where there are numerous setae 

 having a modified muscle apparatus, or none, or where the setae have 

 disappeared altogether. 



In my 1946 key I omitted Sluiterina Monro, 1927, and used Para- 

 honellia Onoda, 1935, instead of Ikedella Monro. I had not then seen 

 the figures published by Wesenberg-Lund (1934, p. 8) and Stephen 

 (1941, pi. 8, fig. 1) clearly demonstrating that Hamingia arctica has a 

 terminally bilobed proboscis, not at all thalassemoid, as Monroe, I, 

 and others had supposed. 



SYNOPSIS OF GENERA OF BONELLimAE 



a '. Nephrostome situated at base of nephridium. 



6 \ Proboscis not branched or cleft at tip ; absent in NelloUa. 

 c \ Two nephridia. 

 (i\ Female with 2 well-developed setae; anal vesicles wide sacs provided 

 with a very large number of slender excretory tubules having apical 

 funnel ; dorsal vessel of vascular system in direct connection with 

 neurointestinal ; male unknown. 

 e \ Proboscis without specialized funnel at its base ; nephridia opening to 

 exterior by separate pores ; external ends of setae can retract into 



a common bursa Maxmiilleria Bock, 1942 



e'. Proboscis with a specialized cup or funnel at Its base; nephridia 

 opening to exterior by a single median pore ; no bursa into which 



ends of setae retract Prometor Fisher, 1948 



d ^ No setae ; anal vesicles more or less rudimentary, the branched tubules 

 opening directly into thin-walled cloaca ; dorsal blood vessel not 

 directly connected with neurointestinal ; body wall extremely thin ; 

 a specialized genital slit (see Acanthohamingia) extending for- 

 ward from nephridiopores and forming a rudimentary androecium 

 for parasitic males, which are provided with anterior curved setae ; 



proboscis unknown Amalosoma ^ Fisher, 1948 



c '. One nephridium. 

 d *. Setae 2, well developed ; anal vesicles 2, elongate, dendritic ; male 



unknown Protobonellia Ikeda, 1908 



d '. Setae 8-10 tiny integumentary spinelets, without muscle apparatus, 

 situated in genital slit extending forward from nephridiopore ; body 



wall thin; males without setae Acanthohamingia Ikeda, 1910 



d '. Setae absent. 



e \ Skin thick, glandular ; in place of proboscis a short truncate snout ; 

 voluminous branched anal vesicles present, the branchlets carrying 



^ Placed in this section because Amalosoma is close to Acanthohamingia, wliich has a 

 Thalasaema-like proboscis. 



