566 DR J. STUART THOMSON ON 



Alcyonium purpureum, Hickson. 

 Plate III. fig. 16 ; PI. IV. figs. 24 and 25. 



This description is based on several large colonies. The largest specimen was 

 roughly hemispherical in shape, and measured 68 mm. in length, 55 mm. in breadth, 

 and about 27 mm. in height. 



The base of the colony was attached to a Tethya-like sponge. The colony 

 consisted of a number of lobes, over 40 in the large specimen, each lobe measuring 

 from 10mm. in height and 6 mm. in diameter to 19 mm. in height and 7 mm. in 

 diameter. The lobes of the colonies have no stalks or trunks, but are connected with 

 one another by a flat encrusting coenenchyma provided with many spicules on its 

 upper and a few spicules on its lower surface, and containing internal canals which pass 

 into connection with those in the interior of the lobes. The colour of the colony in the 

 living condition is brilliant purple, the tentacles being brown. 



The polyps show a tendency to a spiral arrangement on the surface of the 

 ccenenchyma. The number of polyps in the larger lobes is 30 to 40. They are 

 completely retractile within the coenenchyma, and are thus protected by a dense 

 framework of spicules. None of the polyps in my specimens were completely expanded, 

 but those fairly well extended measure from 3'8 mm. in height and 1 mm. in 

 diameter to 4 mm. in height and 2 mm. in diameter. The retracted polyps measure 

 from I'l mm. in height and I'O mm. in diameter down to minute fractions of a 

 millimetre. The polyps are differentiated externally into two parts, a crown and 

 a stomodseal part. 



On the crown, the spicules are arranged in eight triangular areas, pointed above. 

 They appear to be arranged en chevron, but more irregularly than in the typical en 

 chevron arrangement. The spicules of this part are mostly spindles. The spicules 

 protrude on the surface of the polyp, but this is more especially the case on the 

 stomodseal part, where this feature is very apparent. On the stomodseal part, the 

 spicules are arranged in eight parallel bands, whose bases pass gradually into the 

 general surface lying between the different polyps. There appears thus to be a gradual 

 transition from the base of the polyp into the rind of the ccenenchyma, and no 

 differentiation into a calyx. The spicules of the polyp are numerous, and protrude so 

 much on the surface as to produce roughness to the touch. With a low power, the 

 external surface of the stomodseal part appears as if studded with small rough 

 tubercles which are the protruding heads of clubs, spheres, and double spheres. In 

 spirit, the spicules are of a coral-white colour. 



Transverse sections through the polyp show that the muscles are well developed, 

 the siphonoglyphe is ciliated, the mesenterial filaments are well developed, and the 

 dorsal and ventral intermesenterial cavities are slightly smaller than the other six. 

 The ciliated groove is directed towards the external ccenenchyma or rind. The 

 coenenchyma contains about a dozen canals. The rind of the coenenchyma contains a 



