260 Rev. T. Hincks on the 



is probably characteristic of the species. In its earliest stage 

 it is simply acicular. 



The spines are variable in number, but the full normal 

 equipment seems to be three on the outer and two on the 

 inner margin. 



The front avicularia are usually present and often of 

 gigantic size, covering almost entirely the portion of the cell 

 below the aperture. In some cases, however, they are quite 

 insignificant ; internodes occur occasionally on which all the 

 appendages are reduced to mere pygmies. I have seen a 

 considerable section of the stem, including several internodes, 

 on which scarcely one was present and none strongly deve- 

 loped. It is quite possible therefore that they might escape 

 the notice of an observer who had not the opportunity of 

 examining a number of specimens. 



Family Bicellariidae. 



BuGULA, Oken. 



Bugula calathus, Norman. 



This species occurs in the Adriatic and is at once recog- 

 nized by its characteristic habit of growth and its light colour 

 when dried, apart from the minute structural differences by 

 which it is separated from B.jlahellata. 



Bange. Britain (south-west) and Channel Islands. 



Bugula ditrupcE^ Busk. (PI. IX. fig. 3, 4.) 



The form which is represented in figure 4, Plate IX., is 

 probably referable to this species, tJiough it differs in some 

 points from Busk's description. The cells can hardly be 

 regarded as " fusiform ; " they taper gradually and slightly 

 downward, but are not contracted above. The spines, which 

 are very constant in number and arrangement, do not corre- 

 spond with those of B. ditrupoe as described. On the outer 

 margin, which is somewhat folded in, are two spines, one of 

 them suberect and pointing upwards, the other originating 

 close to its base and curving slightly outwards. A similar 

 pair is placed at the top of the inner margin. Immediately 

 behind the outer pair on the top of the cell is a tall spine of 

 much stouter build than the rest, whilst another, of more 

 slender proportions, rises about halfway between the lateral 

 groups. This is a very characteristic armature, and it is, as 

 1 have said, remarkably constant. Busk assigns four spines 

 to his species, three on the outer and one on the inner margin ; 



