Austrcdian Hydro ids. 345 



The liydiocladia are so delicate as to appear like u fringe of 

 fine cilia, and the hydrothecae far too small to be conspicuous to 

 the naked eye; the habit is correctly show.n in Kirchenpauer's 

 figure (which agrees exactly with a drawing by Mr. Busk), and 

 therefore dift'ers widely from AUman's figure. 



Plumularia rotunda M. and T. (Plate XVII, Fig. 1). 



riiunularia ddicatida car. rotunda, Mulder and Trebilcock,, 

 Geel. Nat. (2), iv., 1911, p. 116, pi. ii., fig. 2. 



Hydrucaulus monosophonic, pinnate, stem divided into long: 

 internodes, each bearing a hydrocladium but no hydrothecae. 

 Hydrocladia alternate, borne near the summit of the stem-inter- 

 nodes, the first internode short, without appendages, the others, 

 alternately long and short, only the former bearing hydrothecae. 



Hydrothecae elliptic, lying along the internode, front wall 

 arched, becoming thicker towards the aperture, where it is in- 

 curved ; aperture small, oblique, margin concave at the sides, 

 not everted, back entire, free. 



Sarcothecae bithalamic, canaliculate, one below each hydrotheca 

 and two lateral above, one on each intermediate internode, one (or 

 two?) in each axil, and one on the lower part of each stem-inter- 

 node, median ones stout and fixed, laterals thinner, moveable? 



Gonosome. 1 



Loc— Bream Creek, Pt. Phillip, (M. and T.). 



I have only seen one specimen, which was abt)ut 3 mm. in height^ 

 but was incomplete. It is most nearly related to P. delicattda and 

 P. setaceoides so far as the trophosome is concerned. The portion- 

 of the hydrothecal internode above the hydrotheca is often divided" 

 off by a distinct constriction. 



The most characteristic feature is the form of the hydrothecae,. 

 whicli in side view are considerably stouter than those of P. 

 delicafuln, with the base more elevated; while the incurved 

 thickened lip is also peculiar. In P. delicafyla the border is 

 convex at the sides, in P. rotunda it is concave, and more con- 

 tracted. Only one sarcotheca was seen in each axil, but as in one- 

 case it was at the back instead of in front, it is not unlikely that 

 there may have been originally two. On the processes supporting 

 tlie hydrocladia thin places could l)e detected, with apparent aper- 

 tures, but not forming distinct mammilliform prominences, as \n 

 many species. 



