318 ERNEST WARREN. 



are provided with a sharply defined distal ridge and a flat 

 or slightly convex upper surface {op.). The mature female 

 gonangium is more elongated, and is irregularly ridged about 

 the middle. As in the case of the male gonangium the 

 blastostyle does not produce well-defined gonophores, but the 

 ova may be seen in a cluster on one side (text-fig. 13, B, hi.). 

 Ultimately the eggs or young planulte are extruded into a 

 kind of marsupial case, which appears to be formed by a 

 secretion produced by the blastostyle at the base of the 

 depression containing the egg-cluster (B). I am not aware 

 that such a structure has been previously recorded among 

 the Plumulariidas. 



Systematic Position. — This species is certainly very near to 

 Plumularia setacea {Ellis) of Europe and America. The 

 gonangia, however, appear to be sufficiently distinct to 

 warrant the formation of a new species. The male gonangium 

 in P. tenuis is much larger than the female, while the 

 reverse is stated to be the case in setacea, also the occur- 

 rence of the marsupium-like structure in the female is 

 characteristic. 



(23) Antennella natalensis sp. n. 



This exceedingly delicate hydroid grows on sea-weeds and 

 worm-tubes. It does not appear to be very common on the 

 Natal coast. 



Trophosome. — Hydrorhiza, irregular reticulum, diameter 

 0'09 mm., thickness of perisarc 15 ju. 



Hydrocaulus. — There is no main stem, the "pinnas" or 

 hydrocladia springing directly from the creeping stolon. The 

 hydrocladia are regularly divided into internodes, alternate 

 ones carrying hydrothecae. The node immediately below a 

 hydrotheca is exceedingly oblique, that above is transverse. 

 Nematophores ; a mesial one below each hydrotheca, a median 

 nematophore with very thin-walled sarcotheca immediately 

 above each hydrotheca, two supra-calycine nematophores 



