766 SOME NEW AND RARE HYDROIDA IN THE AUSTRALIAN MUSEUM, 



length, each bearing a hydrotheca on its upper part. Hydrothecie 

 adnate nearly half their height, large, stout, cylindrical, smooth, 

 usually somewhat rounded at the base, curved outwards ; aperture 

 looking outwards and upwards, not contracted, margin entire, 

 very slightly everted, peristome often double or triple. 



Gonothecse unknown. 



Hob. Port Jackson. 



A single specimen occurred among a mass of S. divaricata var. 

 sub-dichotoma. It is quite unlike any Australian species hitherto 

 known, and may be readily distinguished by the uncontracted 

 entire margins of the hydrothecse. The latter somewhat resemble 

 those of Sertularia patula. Busk, but are free for a much greater 

 portion of their length. I could not satisfy myself of the exist- 

 ence of an operculum. 



SYNTHECIUM, Allman. 



The genus Synthecium differs from Sertularia in the gonosome, 

 the pedicels of the gonarigia having their origin within certain of 

 the hydrothecse, where they take the place of the hydranths. The 

 Sertularia ortkogonia of Busk, the gonosome of which has hitherto 

 been unknown, belongs to this genus, so also doubtless does 

 S. patula. The Dynamena tubulosa, Heller (Zoophyten mid 

 Echinodermen des Adriatischen Meeres), is evidently a Synthe- 

 cium. Professor Allman has remarked that Heller's figure shows 

 a gonangium springing directly from the stem, but I have no doubt 

 that what Heller has figured is a parasitic hydroid like Campan- 

 nularia (?) costata. 



The five known species all agree in having opposite pinnse, 

 which spring from the stem at a point where there are no hydro- 

 thecse, also in having the hydrothecse opposite, tubular, curved 

 outwards, and with the margin entire. Professor Allman's two 

 species (which are probably reducible to one) have the hydiothecae 

 very much slenderer in proportion to the length than S. ortkogonia 

 and S. patula (which may perhaps be also united). Heller's 

 species is likewise very similar to S. patula, and may be identical. 



