383 



III. " Brief Description of a Ctenostomatous Polyzoon, allied 

 to Vesicularia, occurring on the Australian Coast." By 

 JOHN DENIS MACDONALD, Esq., Assistant Surgeon R.N. 

 Communicated by Captain DENHAM, R.N., F.E.S. Re- 

 ceived January 13, 1857. 



In one of our visits to Moreton Bay, the scan was hauled at More- 

 ton Island, and amongst the masses of sea-weed, &c. brought up 

 with the net, I found numerous specimens of a very beautiful Poly- 

 zoon, a small portion of which I had previously dredged at Port 

 Stevens from a depth of 5 or 6 fathoms. 



The Polypidom may be said to have consisted mainly of rooted, 

 spreading and plantlike portions, and short, straight creeping trunks, 

 connected at both extremities with the fixed part of the former, so 

 that the whole presented the appearance of an open lace-work, having 

 all the transparency and lustre of glass. 



The trunks and branches were nearly perfectly cylindrical, and 

 composed of an outer membranous sheath distended with a clear 

 fluid (which escaped with considerable force when the sheath was 

 ruptured), and line-like reticulated vessels disposed in one plane, so 

 as to communicate laterally with the polyp-cells, and divide the axis 

 longitudinally into equal halves. The more central canals of this 

 vascular plane combined to form a compound vessel, which opened 

 into a. spherical sinus with cellular parietes at the base of each 

 branch. 



The ramification of the Polypidom generally exhibited a trichoto- 

 mous arrangement, with simple articulations occurring onlv where the 

 branches were given off. 



The cells were clustered in linear series on opposite sides of the 

 branched axis, oval in shape, corneous in texture, with a terminal 

 combed aperture, folding inwards by the contraction of four equidi- 

 stant sets of muscular fibres, which imp.irted a quadrilateral figure to 

 the opening. 



The polypes were very minute, but exhibited distinctly all the im- 

 portant points of structure observable in those of Vesicularia and 

 Bowerbankia, between which genera this polyzoon would appear to 



