THE STRUCTUEE OF XENIA HIOKSONI. 247 



former character is due to the fact that their spicules are very 

 minute rounded or oval discs, which have an organic basis 

 impregnated witli only a small quantity of calcium carbonate. 



This colony arises from a single stem^ which is slightly 

 expanded at its point of attachment to the rock, and measures 

 about 15 mm. in diameter at that point. This basal portion is 

 very short and thick, and supports four main stems, all of 

 which divide into two or more, producing altogether thirteen 

 stems or branches ranging in length from about 10 mm. to 30 

 mm., and in breadth from about 4 mm. to 10 mm. The total 

 height of the colony from the point of attachment to the tips 

 of the highest polyps is 50 mm. 



The polyps are, for the greater part of their length, bound 

 together in bundles of about forty to sixty, each bundle forming 

 one stem of the colony. The free portions of the polyps arise 

 from the slightly expanded umbrella-shaped area at the distal 

 end of each stem. Many of the polyps stand almost perpen- 

 dicularly to the convex disc, but those near the edge of the disc 

 hang downwards towards the base of the colony. The polyps 

 are closer together near the edge of the umbrella, being here 

 '5 mm. to "7 mm. apart, whereas in the middle of the umbrella 

 they are 1 mm. to 2 mm. apart. 



Polyps (PI. 24, fig. 2). — The polyps, or, more correctly, 

 the free portions of the polyps, are non-retractile and mode- 

 rately long and slender. The tentacles are half to two thirds 

 as long as the body of the polyp. Each tentacle bears on its 

 inner side numerous short, conical elevations with rounded 

 ends. These correspond to the pinnules found on the tentacles 

 of other Alcyonaria. 



The colour of the colony in spirit is light brown. 



As mentioned above, the free portions of about forty to sixty 

 fully developed polyps project from the umbrella-shaped area 

 at the distal end of each stem, but besides these there are several 

 younger polyps or buds in various stages of development, and 

 these are invariably situated on the edge of the umbrella. 



In fully developed specimens the following are the measure- 

 ments : — "Body " of the free portion of the polyp 4 mm. to 



