94 BICELLARIIDiE. 



cosa, and which Loven subsequently distinguished as B. 

 quadridentata, presents a striking contrast in general 

 aspect to the normal B. Murrayana. Its slender habit 

 and mode of growth are very much those of a Scrupocel- 

 laria ; while the typical form, with its broad truncate seg- 

 ments, reminds us of a Flustra. 



After an examination of the minute characters, how- 

 ever, there can be no doubt that the two are referable to 

 one and the same species. The variety owes its very 

 marked facies simply to a reduction in the number of the 

 rows in which the cells are disposed. The other struc- 

 tural characters are the same in both, with the single 

 insignificant exception that the marginal spines are less 

 numerous in the form fruticosa. The case is an inter- 

 esting one as showing how completely the external ap- 

 pearance of a species may be changed without the modifi- 

 cation of a single essential character. 



The shoots at their origin are uniserial, three or four 

 cells being linked together, as in Eucratea, 



On the dorsal surface the cells appear of a somewhat 

 fusiform shape (^' en forme de barillet,^^ Van Beneden), 

 separated by deep furrows, and marked here and there 

 by transverse black and white bands. The surface is 

 smooth and shining. On each of the marginal cells there 

 is a pore placed on the back a little below the spinous 

 process on the outer angle, which marks the point from 

 which, in the lower part of the shoot chiefiy, the 

 radical fibres originate. Above they are but rarely deve- 

 loped. 



The long and remarkably stout radical fibres are deve- 

 loped in great profusion ; they attach themselves by 

 means of a number of fibrils given off from the free 

 extremity, which adhere firmly to any neighbouring sup- 

 port. 



