268 Dr. Johnston's 'Catalogue of Zoophytes. 



Hab. On rocks near low water mark, and on the roots of Laminaria digitata, common. 



The spots formed by this species are often an inch or upwards in diameter, every where 

 closely adherent, thin, and rough to the naked eye. The cells are regularly disposed in 

 adjacent rows, and lie on the crust. Their thin walls have a frosted appearance, and, when 

 dry, appear to be perforated with minute holes. Above the aperture, and a little removed 

 from the margin, there rises up a blunt white tooth, but the margin itself is not toothed : 

 it is circular, and on each side of many of them there is a small triangular slit, which seems 

 to be the aperture of an abortive cell. Many of the cells, in some specimens, are covered 

 with a white conical operculum, which is grooved and opake, and has been considered an 

 ovary. 



2. B. trispinosa, crust white, dotted with yellow, sub-circular, cells radiating from the 



centre ; aperture closed by a membrane, and armed on the lower margin with three 

 long spines. 



Discopora trispinosa, Johnston in Edin. Phil. Journ. xiii. 222. 



Hab. On the shell of Lithodes spinosa. 



A thin, calcareous, sub-circular, layer three-quarters of an inch in diameter, affixed by 

 its whole basis, but when dry easily removable ; of a white silvery colour, with minute yel- 

 low dots. Cells in rows radiating from the centre, small, horizontal, with a raised round 

 aperture, which is closed by a brown membrane, whence the dotted surface it presents to 

 the naked eye : the cells are divided on the upper side, and on the lower armed with three 

 long, stout, conical spines. Dr. Fleming unites this with the preceding, but, as I think, 

 erroneously. I regret that I cannot give a figure of it, for the specimen, from which the de- 

 scription was taken, was presented to Mr. Gray, of the British Museum, nor have I since 

 met with another. 



3. B. utriculata, crust white, irregular ; cells adjacent, almost globular, frosted, the aperture 



contracted, circular, armed with spines longer than its own diameter (tab. nost. xii. 

 fig. 6). 



B. utriculata, Flem. Brit. Anim. 533. 



Cellepora ciliata, Lamour. Corall. 41. 



Hab. On Shells from deep water. Our specimens are on Mytilus modiolus. 



The crust is thin and closely adherent, so that it cannot be removed from its foreign 

 base. The spines of the aperture are marginal, and are easily broken off, whence it is rare 

 to find them perfect except near the margin of the crust, or when this lies protected by 

 some inequality of the surface which it grows upon. They are about five in number, and 

 almost equal the cell in length. 



5. B. flava, crust yellow, glazed, irregular ; cells immersed in the crust, with contracted 

 slightly projecting circular apertures, armed with three spines on the under side. 



Hab. On a piece of Limestone from deep water. 



The crust is thickish and uneven, and, when dry, may be detached in pieces from the 

 foreign base. The spines of the aperture are almost always broken off, but the species is 

 otherwise well characterised. 



