296 ERNEST WARREN. 



SERTULA.RELLA PUSiFORMis {Hiiichs), Hiucks, T.. 'A Histoiy of tlie 



Britisli Hydroid Zoophytes,' 

 p. 243; Havtlatib, CI., 'Hy- 

 droiden aiis dem Stillen Ocean 

 Zool. Jalirbiicher,' a^oI. xiv, 

 Jena, 1901, p. 372; Nutting. 

 C. C, ' American Hydroids,' 

 pt. ii, " Sertularidse," 1904, 

 p. 89. 



As in tlie case of the last species, the identification of the 

 present species with S. f usif ormis can only be regarded as 

 provisional^ until the limits of variability in f usif ormis are 

 more definitely known. 



The Natal hydroid is found on sea-weeds or creeping on 

 larger hydroids. It is considerably smaller than S. poly- 

 zonias, the stems not being more than about one quarter of 

 an inch in height. It is pale-brown in colour. 



Trophosome. — Hydro rhiza consists of an irregular, creep- 

 ing stolon, sparingly branched. 



Diameter about 0"15 mm. ; thickness of perisarc 0"018 mm. 



Hydrocaulus. — The stolon produces upright stems, which 

 have never been found to branch, and they carry from 6 to 10 

 hydrothecee. 



The stem is distinctly zig-zag, and is divided by faint 

 oblique divisions into internodes, each bearing a hydranth. 

 The base of each internode is ridged by one, or by one and a 

 half, spiral tarns (text-fig. 5, C) . 



Diameter, measured close to the base, about 0"130 mm. ; 

 thickness of the perisarc 20 ;u. 



Hydrotheca. — Alternate, ventricose, adnate for about 

 half its length to the hydrocaulus. It is less divergent, 

 and the quadrangular mouth is less expanding than in S. 

 p o 1 y z o n i a s. The adcauline free surface is sometimes slightly 

 ridged (r). 



There are four teeth, and the operculum consists of four 

 flaps. There are no internal knobs of chitin constricting the 

 mouth, as occur in the Natal specimens of 8. polyzonias. 



