312 EENEST WARREN. 



Total length 1*70 mm., length of spines 0"39 mm., greatest 

 breadth 0"59 mm. 



Systematic Position. — The description of the Natal hydroid 

 differs from that given for hi dens from Anstralia in the 

 following characters : 



(1) The mnch greater size of the sharp angles of the 

 gonangia. 



(2) The relative shortness of the hydrotheca. 



(3) The presence of internal knobs of perisarc near the 

 margin of the mouth. 



(4) The colony is pale brown. 



Taking the characters altogether, the Natal hydroid appears 

 somewhat intermediate between Bale's S. maplestonei and 

 his S. bidens. The internal knobs of perisarc are not men- 

 tioned; but we know from other species that their presence 

 or absence cannot be regarded of specific value. It is possible 

 that the Natal hydroid, S. bidens and S. maplestonei are 

 varieties of the same species ; but a direct comparison of a 

 series of specimens would be necessary for arriving at a 

 definite conclusion. 



(20) Pasythea qnadYidentata {Ellis & Sol). 



Sertularia quadridentata EUis and Sol. ' Zoopli.,' 1786, p. 57. 

 Pasythea quadridentata (EUis and Sol.). Bale, W. M.. 'Cat. of 



Australian Hydroid Zoophytes,' 1884. 



p. 112 ; Niitting, C.C., 'American 



Hydroids,' pt. ii, '' The Sertularidse," 



1904, p. 75. 



The hydroid grows on sea-Aveeds; it is yellowish-brown and 

 about I inch in lieight. 



Trophosome. — Hydrorhiza forms a wide-meshed reticu- 

 lum. It is characterised by possessing internal ribs of peri- 

 sarc which project into the cavity from the vertical sides, and 

 appear from above as pegs which extend internally for about 

 one quarter to one third of the diameter of the hydrorhiza 

 (text-fig. 11). The presence of these pegs renders the hydro- 



