with Notes on Bicellaria Grandis. 45 



the lamina between the mouth and the two suboral orifices, 

 though calcareous, is easily destroyed by excess of heat, 

 showing the interior of the cell as a single chamber. I have 

 endeavoured to show this in the figure accompanying this 

 paper.* 



Sub-order CYLOSTOMATA, Busk 



Family Hornerid^e, Hincks. 



Genus Hornera, Lamouroux. 



Hornera subdubia, n. sp. Plate II.; Figs. 6, 7, 8. 



Zoarium irregularly branched, seldom inosculating ; cells 

 few, terminal on minor branches or pinnae bestowed laterally, 

 produced and tubular ; orifice simple or slightly produced 

 on one side ; zoarium punctured on front and back ; both 

 surfaces faintly fibrillate ; ovicells raised, globular, or 

 conical, scattered freely over anterior surface. 



Locality. — Marion Islands. " Challenger" Expedition. 



This is a very strange form, owing to the small number of 

 cells. The specimen I have is one inch long, and the same 

 in width ; it does not look like the old base of a colony, but 

 has all the fresh appearance of a terminal portion. The 

 scarcity of cells is remarkable, particularly when we regard 

 the large number of ovicells, which literally cover the whole 

 specimen. Occasionally a single tubular cell is to be seen 

 on the side of the main stem, but the majority are only 

 found on the ends of short lateral pinna?, in companies of 

 two, sometimes only one ; and in most cases the orifice is 

 closed as if by a calcareous deposit, or an operculum (!). A 



* I was induced to make this comparison because Steganoporella smittii, 

 Hincks, assumes the habit of a Vincularia on the north coast of Australia. 

 I have specimens from Port Darwin showing every stage from the ordinary 

 encrusting form, through the free, erect, hemescharal, and escharal forms. 

 This change of habit I consider to be a sort of mimetism, which will be 

 enlarged upon on another occasion, when I propose to show the importance 

 of true zoarial habit as distinct from mimetic changes of form. 



I may here indicate West Australia as another locality for Steganoporella 

 smittii. Two valves of Tridacna from that coast in my possession are 

 encrusted by large colonies of this species, agreeing exactly with the 

 description by Hincks of the Cornish form, except that the foramina in the 

 West Australian form are very much larger, showing the full extent of the 

 inner chambers ; each orifice being more than half as large as the cell 

 mouth, sometimes quite as large. The front wall of the cell is much 

 depressed across the centre. The very curious avicularia are pretty freely 

 dispersed over the colonies, and the ovicells numerous in patches. 



