572 



DR J. STUART THOMSON ON 



My description is based on several yellow specimens and one red example from 

 different localities. The colony is composed of a massive primary or central trunk 

 which gives off secondary branches, and these in their turn may have tertiary 

 or terminal branches. The following measurements may be noted : 



The polyps are irregularly scattered on the entire surface of the colony, except on 

 the basal part of the trunk. The polyps are completely retractile, and in this condition 

 are covered over by the general surface of the ccenenchyma, which is very abundantly 

 provided with small spicules. The rind cannot, however, be described as hard. There 

 is apparently no calyx. 



In my specimens the polyps were, as a rule, withdrawn, but when not so were seen 

 to be small, colourless, and entirely devoid of spicules. In regard to the system of 

 canals in the coenenchyma, it is that of a typical Alcyonium arrangement. The 

 ccelentera are continued as canal-like tubes down the trunk. In regard to the structure 

 of the polyps, the siphonoglyphe is ciliated and directed towards the exterior or away 

 from the centre of the colony. Neither the muscles nor the mesenterial filaments are 

 well developed. The polyps are almost entirely white, and are devoid of spicules. 

 The number of pinnules in a tentacle is eighteen. 



The spicules of the colony are mostly double spheres ; there are also a few much 

 smaller and more irregular spicules which are more or less oblong, but with a narrowed 

 median part and with four or more spines at the margin. The spicules are distributed 

 in the external coenenchyma of the polyp-bearing part, and in the rind of the trunk, 

 but there are either none or very few spicules in the centre part of the colony. The 

 double spheres of the yellow specimens measure from 0'0256 by O'Ol 89 to 0'0513 by 

 0'0351 mm. The double spheres of the red specimen measure from 0'0486 by 0'0378 

 to 0'0594 by 0'04455 mm. The small, more irregular spicules measure approximately 

 0'0270 by O'Ol 89 mm. The red specimen contains a few yellow spicules, although the 

 majority are naturally red. 



