BY W. M. BALE. 76? 



Synthecium orthogonia, Busk. 

 (Sertularia orthotjonia, Busk, "Voyage of the Rattlesnake.") 



(Plate XVIL, figs. 1-5). 



Hydi'ocaulus pinaate, attaining a lieight of about three inches ; 

 internodes of the stem long, each bearing a pair of pinnae at the 

 summit, and one or two pairs of hydrothecse below (except the 

 lower internodes, which commonly bear a pair of pinnae only) ; 

 pinnse distant, opposite, widely diverge nt, divided into internodes, 

 each AAath one pair of hydrothecse. Hydrotheca; opposite, not in 

 contact but often approximate in front, tubular, adnate most of 

 their height, free part curved outwards more or less abruptly and 

 often produced horizontally ; apei'ture circular, vertical or directed 

 slightly upwards, margin entire, very slightly everted, usually 

 more or less marked with lines of growth. 



Gonothecge large, elongated, somewhat compressed in a plane 

 vertical to that of the hydrocaulus, with about 8-10 distinct ti-ans- 

 verse undulations on the broader sides ; aperture terminal, very 

 small, without thickened border or distinct operculum. 



Hab. — Ofi" Ball's Head, Port Jackson. 



1 have no doubt that this is the Sertularia orthogonia of Busk, 

 though the free part of the hydrothecse is rarely produced outwai'd 

 to so great an extent as in the type form. This abbreviation of 

 the hydrotheca tends to weaken the distinction between thi.s 

 species and S. patula, nevertheless it is still open to doul)t whether 

 they should be united. The hydrothece of S. orthogonia are 

 longer than those of S. patula, and tlie adnate portion is decidedly 

 more erect, while the free part is curved outwards much more 

 abruptly, and the aperture is nearly or quite vertical, even when 

 the terminal portion of the hydrotheca is somewhat ascending. 

 The margin is not noticeably sinuated at the sides, and i.s marked 

 with lines of growth even in the terminal hydruthecio. In *!?. 

 patula the hydrothr-cto are smaller and are not abruptly flexed, 

 but are gradually curved outwards for most of their Uiigth, while 



