764 SOME NEW AND RARE HYDROIDA IN THE AUSTRALIAN MUSEUM, 



SERTULARELLA VARIABILIS, n.sp. 



(Plate XV., figs. 5-9). 



Hydrocaulus simple or pinnate, pinnae when present alternate,, 

 given off just below each hydrotheca on the stem ; stem and 

 pinnae divided by twisted joints into internodes, each bearing a 

 hydrotheca on its upper part. Hydrothecse adnate from J to J 

 their height, divergent, both series directed towards the front or all 

 nearly in the same plane, with several more or less distinct trans- 

 verse rugae, contracted near the aperture and swollen below ; 

 aperture with three marginal teeth, one superior and two lateral, 

 also with three internal compressed vertical teeth alternate with 

 those of the margin, or sometimes with three teeth within the 

 lowest side and one within each of the other two sides. 



Gonothecse ovate, with transverse undulations which vary greatly 

 in number and distinctness, and are often absent from the proximal 

 part ; summit tubular, with from two to six teeth, and a small 

 circular aperture. 



Hob. Bondi ; Coogee. 



With some hesitation, I include under the name of S. variabilis 

 a series of forms allied to (and partly intermediate between) the 

 S. indivisa and S. solidula of the southern coast. The form which 

 may be regarded as the type differs from S. indivisa mainly in 

 having the internodes and hydrothecse stouter and comparatively 

 shorter, so that for the most part each hydrotheca is nearly or 

 quite in contact with the lower part of the next internode above, 

 while in S. indivisa the intern odes are slender and elongated, with 

 the joints consisting usually of double oblique constrictions, so 

 that the hydrothecse are more widely separated. The hydrothecse 

 in the present form are also larger, and both series are commonly, 

 but not invariably, directed towards the front, instead of lying in 

 the same plane. The other principal type represented in the 

 collection seems more apt to assume the pinnate form, and would 

 not be suspected of any very close affinity with the first variety 

 if it were not for the occurrence of intermediate forms. The 



