AJiTD SPECIES OF nTDEOIDA. 271 



which they give a somewhat prismatic foi'ni, constitute also a 

 striking feature. 



Only a single specimen of this species was contained in the 

 collection. Its main stem was quite simple ; and this is probably 

 the general character of the species. Its hydrorhiza was not 

 present. 



Thuiaria cerastium. Plate XVIII. figs. 3, 4. 



Tropliosome. Hydrocaulus attaining a height of about two 

 inches, springing from a bundle of entangled tubular filaments, 

 simple for some distance from the hydrorhiza, and then becoming 

 dichotomously branched with great regularity ; simple portion of 

 hydrocaulus and its more proximal subdivisions fascicled, the rest 

 of the subdivisions monosiphonic. Hydrotheceae tubular, with 

 entire orifice, adnate to the hydrocaulus in their entire length, 

 alternate ; hydrothecse of each series closely approximate to one 

 another, directed alternately (when viewed from the free side) to 

 the right and to the left. 



Gonosome. Gronangia springing singly by a narrow point close 

 to the angle of each subdivision of the dichotomous stems, broadly 

 obovate, strongly annulated, opening at the broad distal end by a 

 narrow tubular projection. 



Locality. Northern Island, New Zealand, Dr. Andrew Sinclair, 

 JkTr. Busk's collection. 



The very regular dichotomous ramification, with the gonangia 

 situated in the axils of the branches, gives to this species a very 

 striking aspect, and strongly suggests the form of inflorescence 

 met with in certain common caryophyllaceous plants. 



Thuiaria persocia lis. Plate XVII. figs. 4-6. 



Tropliosome. Hydrocaulus attaining a height of about 2\ 

 inches ; main stem undivided, monosiphonic, sending ofi" along 

 its entire length pinnately disposed opposite ramuli, and having 

 a well-marked transverse joint between every pair of ramuli ; 

 ramuli with a joint here and there at irregular intervals. Hy- 

 drothecae deep flask-shaped, with entire, semielliptical orifice, those 

 of each series separated from one another by scarcely any interval 

 on the pinnae, more separated on the main stem, subopposite, or 

 opposite on the pinnae, more decidedly opposite on the common 

 stem. Axis of pinnae frequently extended beyond the distal 

 extremity as a cylindrical tube, destitute of hydrothecae, and 

 serving for attachment. 



