HVDROIDA. BALE. 15 



may be succeeded by a fe\v internodes with a single pair. The 

 upper hydrothecae have not the subtubular ascending habit found 

 in the type form, nor do the pinna? run out into long tubular 

 prolongations. A similar variety has been found at Portland. 



The jointing of the base of the pinnae varies greatly in this 

 species. In some individuals the apophysis has a very strongly- 

 marked transvei'se node in the middle, then it is separated from 

 the pinna by a conspicuous oblique joint, the pinna running down 

 to a sharp point in front of the apophysis, which is continued 

 upward into a similar point. But specimens occur in which these 

 joints are scarcely marked, or even indistinguishable, so that the 

 pinna appears continuous with the stem. Intermediate forms 

 are found, and even in the same specimen the joints may vary 

 considerably in distinctness. 



The two species which most resemble 8. macrocarpa in the 

 form of the hydrotheca? are 8. bldeiis and 8. recta. 8. bidei/s 

 is smaller in all its parts, with sharper teeth on the hydrotheca- 

 margin ; it is also distinguished by the presence of a small 

 chitinous projection inside the apocauline wall of the hydrotheca, 

 and the absence of the distinct tooth inside the aperture ; while 

 the gonangia are of totally distinct forms in the two species. 



The likeness to 8. recta is, in regard to the trophosome, rather 

 closer. The unusual feature of the latter species, noted in my 

 first specimen, is also found in the only other example which I 

 have seen, namely the situation of the two series of hydrotheca 1 

 in a single plane, so that there is no distinction of anterior and 

 posterior aspect to the polypidom, I do not however lay too 

 much stress on this, knowing that in some hydroids there is much 

 inconstancy in this particular. The pinna? of 8. rertii stand off 

 from the intei-uodes at right angles, while those of 8. macrocarpn 

 form a somewhat smaller angle with the stem. The stem- 

 internodes of 8. recta are however more strongly zig-zag, so that 

 the inclination of the pinnae to the general axis of the stem is 

 much the same in (he two species. In 8. macrocarpa the 

 axillary hydrotheca? diverge from the stem at about the same 

 angle as do the pinna?, so that they lie along the latter ; in 

 8. recta they stand out midway between the stem and the 

 pinnae. The internal tooth found in the hydrotheca of 

 S. macrocarpa is not present in 8. recta. I have had some 

 doubt as to whether the two species might not prove to be con- 

 nected, but according to Bartlett's observations the gonangia of 

 8. recta are wholly unlike the large smooth form of those of 

 8. macrocarpa, being furnished with annular transverse ridges 

 similar to those found in many species of Sertularella, 



Luc. Bass Strait. 



