774 SOME NEW AND RARE HYDROIDA IN THE AUSTRALIAN MUSEUM, 



anterior sarcothecse are quite disconnected from the hydrotheca?, 

 and bear a considerable resemblance to the corresponding organs 

 in some of the Eleutheroplea. To that section, therefore, I would 

 assign the new genus, more especially as the only Plumularian 

 which is known to share with A. productum the peculiarity of 

 possessing decumbent adnate gonothecse (namely, Plumularia 

 filicaulis] is an undoubted Eleutheroplean. 



The generic name Azygoplon has already been applied by 

 Professor All man to another hydroid, for which, however, the 

 name Halicornopsis had priority. 



AZYGOPLON PRODUCTUM ( = Plumularia producta, Bale). 



(Plate XIX., figs. 1-5). 



From an examination of specimens obtained by Mr. Whitelegge 

 at Coogee, I am able to give a more complete account of this 

 species than has hitherto been possible, the gonangia in particular, 

 not having been previously observed. These are given off from 

 the hydrorhiza, and are attached to the supporting substance by 

 the flat under side, like those of Plumularia filicaulis and the 

 whole hydrosoma of Lineolaria. The upper side is convex, and 

 furnished with transverse undulations, which vary in distinctness, 

 but do not appear to be ever very strongly marked ; they are 

 usually indistinguishable when seen from above in a fluid medium, 

 but are readily seen by reflected light when dry. The gonotheca^ 

 are large in size, of an irregularly ovate outline, and there is at 

 first no trace of an aperture, but after a certain time a rather 

 large circular area of the capsule close to the distal end appears as 

 if bulged in, forming a slight concavity bounded by a circular 

 ridge at which separation ultimately takes place. 



I have not alluded to the cauline sarcothecae in former descrip- 

 tions of this species, as I failed to see them satisfactorily in my 

 first specimens, owing to their rudimentary condition and the 

 wrinkling of the delicate perisarc ; but I have been able to make 

 them out in other cases, and particularly in Mr. Whitelegge's 

 specimens. There are usually two at the base of each pinna, one 



