172 



HVDROIDA II 



monosiphonic main stem, which not infrequently appears to be dichotomously branched. The bran- 

 ches and the hydrotlieca stalks are ringed close above their origin, and below the hydrothecse, other- 

 wise smooth. The h},'drotheccc are twice to three times as long as broad, cylindrical, or rather inversely 

 conical, passing over by an evenly curved transition into a short, almost c}-lindrical basal part; the 

 basal chamber is small, bounded at the top by a fine, well developed diaphragm, often somewhat 

 ass\inetricallv placed. The hydrotlieca margin is provided with seven to fourteen markedly prominent 

 pointed or pointedly rounded teeth. 



The gonothecce are attached by sliort, ringed stalks proceeding from stem or branches, rarely 

 from the stolons. They are inversely conical or slightly oval, elongated, cut off transversely at the 

 distal end, without neck. The gonophores develope into cryptomedusoid meconidia, projecting from 

 the gonotheca without breaking away. The larval development takes place within the interior of 

 the mecouidium {Goiiof//vr<Ta medusEe). 



Material: 



"Thor" 64°02' N., 22°33' W., depth 34 metres 



Iceland: {without further details) on the back of a Dinriiiattira fcrox taken from a Soii/iiiosns 

 viicroccphalus. 



LaoiJicdca gracilis is a southern visitor to the northern waters (fig. LXXXVIII) where it pene- 

 trates up to the northern point of Norway. The species is altogether of rare occurrence here, but 

 has been taken more especially about the British Isles. One or two finds show that it also occurs 

 sparsely at the Faroe Islands and south-west Iceland, always in the middle or upper third of the 

 littoral region. 



Gen. Bonneviella (Bnxh). 



Stolonial colonies with enormous, often slightly bilateral liydrothecce, having a finely built 

 diajjliragm. The large polyps can be withdrawn entirely into the liydrotheca. The hydranth has a 

 crown of strong tentacles with niultiserial endoderm; the oral part is thin, forming a thin lamella, 

 consisting of two cell-layers, which a little above the tentacle base extend out like a velum in towards 

 the central oral aperture. The tentacle base thrusts itself into the polyp, so that a large proboscoidal 

 cavity is formed between this and the oral aperture. The gastral endoderm is uniformly developed. 



As already mentioned, I am unable to agree with Nutting, who is inclined (1915 p. 94) to 

 support the view advanced by me in a former work (1909 p. 197), that the ectoderm covers the ten- 

 tacle base and the inner side of the velum-like proboscoidal part. Kiihn (191 3 p. 253) is justified in 

 doubting whether the part in (piestion can be reckoned as belonging to the endoderm, and I am 

 more disposed to follow him here, considering the part as an extreme development of the indifferent 

 endoderm cell-layer, as found for instance on the proboscis of Caiiipami/ariithf. The point can, how- 

 ever, only be decided by study of the polyp development. The systematic position of the genus is 

 still altogether doubtful. 



