92 The Genera of the Plumulariidce, 



Gonothecse broadly elliptic, very convex above, with 

 irregular transverse rug^ ; aperture rather large, terminal, 

 looking upward ; margin elevated and expanding, operculate; 

 a number of long, erect spines (usually somewhat over 20) 

 on the upper side of the gonotheca, about equidistant from 

 each other. 



The hydrophyton often commences to grow in a tolerably 

 regular fashion, giving off alternate pinnately-disposed 

 branches, and afterwards forming an irregular network. To 

 the naked eye it resembles very delicate metallic tracery. 

 Most commonly the polypary is more or less invested by 

 minute diatoms and other adventitious matter ; but when 

 this is not the case — as in the newly-formed portions — the 

 structure is perfectly clear and transparent, and of such 

 tenuity as to resemble a soap-film^. When seen by reflected 

 light it is more or less iridescent. 



Sertularia bispinosa, Gray. 



It is noticeable that in this species the older portions of 

 the hydrocaulus are decidedly coarser and stouter than the 

 more recently formed distal portions, a condition which I 

 have not observed in the allied species 8. operculata. 



I have omitted to mention that Professor D'Arcy W. 

 Thompson argues in favour of the identity of the two species, 

 and cites Kirchenpauer's Dynamena fasciculata (which he 

 considers to be Gray's D. bispinosa under another name) to 

 show that there is no more than a varietal difference. This 

 appears, however, to be a misconception, for Kirchenpauer's 

 species is absolutely identical with our common form of >S^. 

 operculata, which differs from the true S. bispinosa in 

 having the calycles adnate for the greater part of their 

 length, and in the form of the gonothecye. 



Such specimens as I have seen of >S^. bispinosa may be 

 readily distinguished from S. operculata by the touch alone, 

 as its coarser habit and sharper serrulations (caused by the 

 more projecting hydrothecae) give it a peculiar harshness, 

 which is very characteristic. 



Mr. H. Watts has collected this species at Warrnambool, 



Sertularia trispinosa, Coughtrey. 



A specimen of this species was collected by Mr. H. Watts 

 at Warrnambool many years since. It has not been recorded 

 from any other Australian localitj^ 



