THE ALCYONARIA OF THE MALDIVES. 495 



former these branches are rather longer and narrower. In <S. grayi (Studer) the grooved 

 branchlets are much longer, more delicate, and pointed or knobbed at the extremity. S. tuhu- 

 losa is therefore as regards its form intermediate in character between S. tortuosum and 

 S. grayi. If we eliminate these characters of form there is, it appears to me, very little 

 to distinguish the species. Now in considering the growth of a form like this we must 

 not leave out of consideration the fact that spirit specimens prove that usually and perhaps 

 always, the tubes of Solenogorgia contain epizoic Crustacea belonging to the genus Alpheus. 

 The general appearance of the groove on one side of the non-tubular terminal branchlets, 

 in specimens similar in form to that described by Studer as S. grayi, suggests that these 

 Crustacea are in the habit of running along them in search of food, and retreating to the 

 tubular parts for protection. The general characters of the groove are the smoothness of 

 the surface as compared with the outer convex side of the branch, the absence of antho- 

 codiae, and the relatively pale colour. These are characteristics which we should expect to 

 find if any part of the surface of a coral were constantly irritated by the feet of an active 

 little crustacean. Now it is well known that in many forms of corals such as Pocillopora, 

 Seriatopora, Millepora, etc. one effect of a symbiotic crab on the growth is the formation 

 of a spherical or oval gall, the margins of the affected part being hypertrophied and gromng 

 round and enclosing the animal that causes the irritation. Similarly, barnacles of various 

 species cause gall-like growths of the coenenchym in various Aladreporaria, Millepora, Gor- 

 gonia, and other Alcyonaria. An examination of the surface enclosed or about to be enclosed 

 by the galls of Pocillopora, Seriatopora, and Millepora shows a smoothness of the surface, 

 and, in Millepora, an absence of polyjjs similar to that shown in the groove of the Soleno- 

 caulon branchlets. 



It appears to me therefore very probable that the tubular character of Solenocaulon is 

 of the nature of a gall produced by an active crustacean, and that the degree to which 

 it affects the secondary and tertiary branches depends, not upon any inherent specific 

 character of the Solenocaulon, but upon the number or activity of the symbiotic Crustacea. 



Whether this explanation is true or not, it is not satisfactory from a systematic point 

 of view to distinguish as distinct species specimens which diifer from one another principally 

 in their form of growth. The many striking similarities that there are between S. tortuosum 

 of Gray, S. tuhulosa of Genth, and S. grayi of Studer in the shape and aiTangement of the 

 spicules and other characters suggest very forcibly that they all belong to one widely 

 distributed species. 



This conclusion receives considerable support from the examination of the very rich and 

 interesting collection of the specimens of this genus made by Mr Gardiner, and I shall 

 therefore place them all, except one which I believe to be the type of a new species, in one 

 species. 



Solenocatdon tortuosum Gray. (Fig. 13.) 



It will be convenient to give in the first place a list of the specimens, with a short 

 description of each one. 



A. A small specimen of a pale pink colour. About 14.5 mm. in height. Stalk 

 75 mm. long, 5 mm. in diameter. Most of the lateral flattened branchlets 

 short. Suvadiva, 43 fathoms. Lagoon. Hard rubble. 



