13$ MANUAL OF ZOOLOGY. 



Alcyonium may be taken as the type of the family, and 

 it is well known to fishermen under the name of " Dead-men's 

 fingers." It forms spongy-looking, orange-coloured crusts or 

 lobate masses, which are attached to submarine objects, and 

 are covered with little stellate apertures, through which the 

 delicate polypes can be protruded and retracted at will. The 

 polypes communicate with one another by an anastomosing 

 system of aquiferous tubes, and the corallum is in the form of 

 cruciform, calcareous spicula scattered through its substance. 

 In the allied Sarcodictyon the actinosoma is creeping and linear. 



FAMILY II. TUBIPORID^. In the Tubiporidce, or "organ- 

 pipe corals/' of which T. musica is a familiar example, there is 

 a well-developed sclerodermic corallum, with thecae, but with- 

 out septa. The corallum is composed of a number of bright- 

 red, tubular, cylindrical thecae, which are united together 

 externally by horizontal plates or floors, which are termed 

 " epithecae," and represent external tabulae. The polypes are 

 usually bright green in colour, and possess eight tentacles 

 each. 



FAMILY III. PENNATULID^E. The Pennatulida, or " Sea- 

 pens," are defined by their free habit, and by the possession 

 of a sclerobasic, rod-like corallum, sometimes associated with 

 sclerodermic spicules. 



Pennatula (fig. 48), or the " Cock's-comb,' ; consists of a free 

 coenosarc, the upper end of which is fringed on both sides 

 with feather-like lateral pinnae, which bear the polypes j whilst 

 its proximal end is smooth and fleshy, and is probably sunk in 

 the mud of the sea-bottom. This latter portion of the coeno- 

 sarc is likewise strengthened by a long, slender styliform 

 sclerobasis, resembling a rod in shape, whilst spicula occur 

 also in the tentacles and ectoderm. The general colour of 

 Pennatula is a deep reddish purple, the proximal extremity of 

 the coenosarc being ^orange-yellow. Our British species (Pen- 

 natula phosphored) varies from two to four inches in length, 

 and is found on muddy bottoms in tolerably deep water. Its 

 specific name is derived from the fact that it phosphoresces 

 brilliantly when irritated. 



In Virgularia- (fig. 49), which, like Pennatula^ occurs not 

 uncommonly in British seas, the actinosoma is much longer 

 and more slender than in the preceding, and the polype-bear- 

 ing fringes are short. The polypes have eight tentacles. The 

 sclerobasis is in the form of a long calcareous rod, like a knit- 

 ing-needle, and part of it is usually naked. No spicula are 

 found in the tissues of Virgularia. In the nearly-allied Pavo- 

 naria the polype-mass is quadrangular in shape. 



