Art. XIV. — Descriptions of New, or Little Known, 

 Polyzoa. 



Part V. 



By P. H. MacGillivray, MA, M.R.C.S., F.L.S. 



[Read 9th August, 1883.] 



In the present communication I propose describing some 

 forms of Retepora, and giving a list of all the Victorian 

 species known to me. 



In this genus the appearance of the cells varies so much, 

 according to age and other circumstances, that the specific 

 determination of fragmentary or imperfect specimens is 

 frequently very difficult and sometimes impossible. Those 

 enumerated here are well-marked, and have definite cha- 

 racters by which I think they can almost always be certainly 

 recognised. 



The habit of growth is not usually of very great value. 

 Of our Australian species, however, several can be recognised 

 at a glance, as R. monilifera (normal form), R. granulata, 

 and R. porcellana. R. munita, formosa, and aurantiaca 

 are very similar in form, but the latter is known by its colour. 

 R. tessellata, Jissa, and avicularis are not easily distinguished 

 from each other without a lens. R. phcenicea is at once 

 known by its permanent red colour. Important characters 

 are derived from the form of the mouth, the structure and 

 situation of the avicularia, the appearance of the ovicell, and 

 in a less degree from the more or less massiveness of the 

 zoarium, and the proportion in size of the fenestras to the 

 interspaces. The ovicell in many species is very character- 

 istic. In R. serrata and avicularis it is filled in, smooth, 

 and without any special markings ; in R. phcenicea the lower 

 part is occupied by a peculiarly-shaped plate, curving down- 

 wards and backwards ; in R. Jissa and aurantiaca there 

 remains a permanent vertical slit, sometimes closed, but 



