26 Proceedings of the Royal Society of Victoria. 



Notwithstanding that there may be some doubt as to the 

 correctness of the diagnosis of this species, owing to its peculiar 

 state of preservation, I have described it because its presence in 

 the Waurn Ponds and Darrimau deposits, and in no other, 

 indicates that these deposits belong to the same horizon. 



(?) Porella minutissima, n. sp. (PI. II., Fig. 20). 



Zoarium encrusting. Zooecia very small, undefined ; surface 

 covered with scattered mamillae. Tliyrostome with a highly- 

 raised subtubular peristome, on the proximal part of which and 

 adherent to it is a tubular process, probably avicularian. 



Locality. — Mitchell River (J. Dennant). 



This is a single specimen and evidently grew round a small 

 cylindrical alga. It is a very small celled species ; the figure is 

 magnified a little more than double the extent of the others. 

 Just above the thyrostome on one side (shown in two of the 

 zooecia figured) there is a small circular opening divided into 

 sectors by radiating ribs, and most of the mamillae have a small 

 perforation in the centre. It is a very puzzling species, and its 

 position is very doubtful, as the primary aperture of the 

 thyrostome cannot be seen ; indeed, I had given up the idea of 

 describing it, but I do so now to bring under notice the very 

 peculiar circular opening near the thyrostome, the like of which 

 I have never seen in a similar position in any species of polyzoa. 



EXPLANATION OF FIGURES. 



Plate I. 



Fig. 1. Catenariopsis morningtoniensis. 



„ 2. Microporella marginata. 



,, 3. Smittia centralis, var. laevigata. 



,, 4. Porella rhomboidalis. 



,, 5. Porella areolata. 



„ 6. Porella otwayensis. 



,, 7. Porella dennanti. 



,, 8. Mucronella proboscoides. 



