270 THE VOYAGE OF H.M.S. CHALLENGER. 



Genus Sympodium, Ehrenb. 



Sympodium, Ehrenberg, Die Corallenth. des rothen .Meeres, p. 61. 



„ Dana, Zooph., p. 608. 



„ Milne-Edwards, Hist. Nat. des Coralliaires, t. i. p. 110. 



,, Kolliker, Icon, histiol., pt. 2, p. 141. 



„ Klunzinger, Die Korallth. des rothen Meeres, p. 42. 



„ Danielssen, Norske Nordhavs-Exped., Alcyonida, p. 141. 



Sympodiadx (pars), Massarella, Sympodium (pars), Gray, Ann. and Mag. Nat. Hist., ser. 4, vol. 

 iii. pp. 119-20, 1869. 



Ehrenberg {loc. cit.) characterises the genus very concisely as follows: — " Basi 

 membranacea, effusa, polypis (in papillas inermes parum prominulas) retractilibus, stipite 

 carentibus." (AntheliaB retractiles.) 



Klunzinger {loc. cit.) emends this diagnosis, pointing out that the polyps are some- 

 times wholly, sometimes only half retractile, and also that the bottom of the digestive 

 cavity is sunk into the basal membrane, a fact which distinguishes Sympodium from 

 those species with membranous bases which belong to Clavularia. 



On a survey of the already known species, the following diagnosis may be given of 

 the genus. From a membranous basis, which grows over foreign bodies, and is penetrated 

 by nutritive canals, polyps arise, whose bodies are more or less deeply sunk into the 

 membranous coenenchyma, but so that they project to a greater or less degree above the 

 basal membrane. The polyps are either at definite distances from each other, or they 

 are associated together in groups round which the coenenchyma thickens considerably so 

 as to raise them above the basal membrane. There are thus formed Alcyonium-like 

 colonies in which the polyps are arranged above each other at various levels. In the 

 part of the polyp which is protruded above the basal membrane, one can always dis- 

 tinguish a calyx-portion, and a more or less retractile anterior region, containing the 

 mouth and the crown of tentacles. The calycine portion is more or less rigid, and is 

 often marked by eight longitudinal ridges, between which are eight longitudinal furrows. 

 The calyx can be closed over the retracted anterior portion of the polyp and then con- 

 tracts into an eight-rayed star. 



The tentacles are frequently armed with spicules, and the oesophageal tube may also 

 contain eight longitudinal bundles of spicules. The form of the spicules varies greatly. 

 Some are smooth, lenticular, others are disc-like bodies ; others are spiny and warty 

 spindles. 



Gray includes among his Sympodiadse, under the generic title Eunoella, Alcyonium 

 gorgonoides, Ellis and Solander. This species Milne-Edwards refers hypothetically to 

 Sympodium, Ehrbg. The figures given by Ellis and Solander (pi. ix. figs. 1, 2, not 

 12 as Gray records), are evidently those of a Palythoa, with distinct twelve-rayed 

 polyps. This form must therefore be expelled from the series of Alcyonaria. 



