BY W. M. BALE. 771 



Pasythea hexodon, Busk. 



Plate XIV., figs. 8-9. 



Hydrocaulus 1-2 inches in height, sub-dichotomously branched, 

 with a hydrotheca in each axil ; internodes tubular, long and 

 slender, bearing the sets of hydrothecse near their upper extremi- 

 ties, joints mostly inconspicuous. Hydrothecse tubular, usually 

 from six to ten in a set, often unequally arranged on the two 

 sides of the internode, each one adnate to that next above it by a 

 considerable part of its dorsal surface, and adnate to the hydro- 

 caulus by its basal portion ; the two series strongly divergent, the 

 lower ones of a set more so than the upper, especially in their 

 terminal portions ; an angular ridge running down each side of 

 the cell ; aperture very oblique (sloped off from below), margin 

 somewhat expanding at the upper part of each side, with two 

 indistinct lateral lobes. 



^06.— Near Peel Island, Moreton Bay (Mr. J. D. Ogilby). 



This species has not hitherto been recorded since Mr. Busk 

 described it in the account of the " Voyage of the Rattlesnake." 

 Mr. Busk says that there are six hydrothecse in a set, but in these 

 specimens there are commonly eight to ten, and sometimes more. 

 While P. quadridentata is closely allied to the Sertulariae, having 

 its calycles in distinct pairs, with the two calycles of each pair 

 in contact in front, P. hexodon, on the other hand, approximates 

 to the Tliuiaria?, the liydrothecai being crowded and overlapping 

 each other, as is so often the case in that genus, while there is no 

 regularity in the arrangement of the two series with regard to 

 each other. In most cases those on the two sides of the hydro- 

 caulus are opposite to each other, but it is quite common to find 

 them alternate, and the set frequently contains more on one side 

 than the other, as three to four, or four to six. The ramification 

 is not perfectly dichotomous, but branches are given off irregu- 

 larly in the same plane, the axial hydrothecse heiiig adnate for 

 most of their length to the principal shoot. 

 50 



