Aet. II. — On Two New Genera of Polyzoa.- 

 By P. H. MacGillivray, M.A., M.R.C.S. 



[Read April 15th, 1880.] 



The two polyzoa which I describe in the present paper are 

 found encircling the stems of Cymodocea antarctica. The 

 first seems to be identical with a form from St. Vincent's 

 Gulf, very briefly described by Mr. Hutton, in the Trans- 

 actions of the Royal Society of Tasmania for 1877, under 

 the name of Membranipora cincta. Mr. Hutton remarks 

 that, from the exact regularity of the position of the cells, it 

 ought, perhaps, to be made the type of a new genus. In 

 addition to, and of more importance than the regularity of 

 the arrangement, the structure of the cells is remarkable ; 

 and although I have placed it provisionally among the 

 Membraniporidse, it will probably be necessary to refer it to 

 a distinct family. The other genus is also a very interesting 

 one, and seems not to have been hitherto noticed. 



Family MEMBRANIPORIDjE. (?) 



Genus Diplopora. 



Polyzoary encrusting; cells occupied by a calcareous 

 membrane in front, and divided into two parts, the posterior 

 half being very much elevated ; a narrow transverse portion, 

 a little distance behind the mouth and in front of the 

 elevated part, deficient in calcareous matter, and entirely 

 membranous. 



D. cincta, Hutton sp. 



The cells are large, oblong, separated by raised margins, 

 and arranged in transverse rows encircling the stems of 

 Cymodocea antarctica, either spirally, or as continuous rings. 

 They also form longitudinal series, occasionally bifurcating. 

 Themouth is large, arched above, hollowed below, with a small 



