256 



from two sides of the main stem and extend in one plane almost perpendicularly, 

 but near the top of the colony where the branches are all about the same length, 

 they stand out in equal numbers in two planes at right angles to one another. 

 The main stem as well as the larger branches again bear twigs in four directions, 

 and this adds to the bushy appearance of the colony. The diameter of the 

 main stem is about 3 mm., that of the twigs about 1-25 mm. 



The ccenenchyma is fairly thick, brown in colour and contains two layers of 

 white spicules. The inner layer is densely })acke(l and the spindles are arranged 

 in all directions. The outer layer is discontinuous, and consists of large rough 

 warty spindles, often .slightly constricted at the middle with swellings on either 

 side ; these are quite visible to the naked eye and are sometimes 3"5 mm. in 

 length. On the older parts they are disposed irregularly, but on the branches 

 and twigs they occur in three or four longitudinal rows mainly on two surfaces, 

 and so give the appearance of white streaks traversing the whole length of the 

 axis ; they often curve and twist around the base of the verrucas. 



On the main stem and larger branches the polyps occur irregularly, young 

 forms arising in no definite manner ; on the smaller branches and twigs they 

 generally occur on the lateral surfaces, but encroach on the other two, though 

 directed laterally. The tip of a twig is occupied by two almost opjiosite 

 polyps with a central dome-like part consisting of the end of the axis covered 

 by the thick ccenenchyma. All stages of development are also found on the 

 younger twigs. 



The verrucce are cylindrical when open, dome-like when closed, lo mm. 

 in height and about 1 nun. in basal diameter. The spicules are arranged in a 

 fairly definite manner, and are intermediate in size between those of the two 

 layers of the ccenenchyma. At the base they are arranged almost transversely, 

 but passing upwards they become grouped into eight bands with an " en chevron " 

 arrangement, the angle gradually lessening until at the top they are almost 

 longitudinal, in pairs of sheaves. When partially open they display eight tri- 

 angular points which fit closely together over the wholly retractile anthocodia3. 



The tentacles are densely covered on the aboral surface with small spindles. 

 These are arranged " en chevron " at the base, but longitudinally higher up. 

 When the tentacles are infolded they touch on the aboral surfaces, and no 

 definite operculum is formed. 



The axis is horny and somewhat flexible ; it is blackish-brown in the main 

 stem but paler in the twigs. The general colour of the colony is light brown, 

 but the large spicules a])pear as white bands. 



The spicules are warty spindles, straight, curved, or S-shaped ; some of the 

 larger forms from the outer layer of the ccenenchyma have a median constric- 

 tion with a swelling on either side. The following are typical measurements 

 length and breadth in millimetres : — 



