GENERA OF THE ALCYONARIA STOLONIFEEA. 337 



The genus includes those Clavulariidse with a thick plate-like stolon into which the 

 polypes may be completely retracted. 



Description of a new Genus (Stereosoma), and of new Species 0/ Clavularia. 



Stereosoma, gen. nov. 



Stereosoma celebense. (Plate XLV.) 



The only specimen of this interesting new genus known to me is one that I found 

 growing on the reefs of Talisse Island in North Celebes. It does not occur in great 

 abundance on any of the reefs that I visited ; in fact the only specimen I found after 

 months of reef-wading in search of specimens was a small colony bearing five or six 

 polypes attached to a piece of water-logged wood. 



The genus can be at once recognized by two important characters, the first being 

 that it shows no power of retracting either its body-wall or tentacles, and the second 

 that the pinnse of the tentacles are separated from one another by very considerable 

 intervals. 



The absence of contractility is a remarkable feature. 



Many Alcyonaria are usually described as not contractile, but the description is 

 seldom perfectly accurate. 



Polypes that possess a great number of densely-packed spicules take a long time to 

 contract, and they may be removed from their habitat, placed in ordinary spirit, and 

 be preserved without showing very much contraction. Again, many Alcyonarians 

 that do not exhibit any considerable power of contracting their body-walls may 

 contract their tentacles. 



Now Stereosoma possesses no spicules, and the tentacles show no more power of 

 contracting than the body-wall. 



The illustration given (Plate XLV.) is a faithful representation of the specimen 

 as it reached England on my return from Celebes, the colour alone having been added 

 from notes that I made at the time of its discovery. 



On making a series of transverse sections through one of the polypes I found that 

 the ectoderm is remarkably thick, and presents a very vacuolated appearance. 



Between the vacuoles and the ectoderm covering the body there may be seen a 

 number of isolated cells, islets of cells, and strings of cells (Plate L. fig. 1). These are 

 undoubtedly derived from the ectoderm, and probably secrete the tough, vacuolated, 

 homogeneous substance that surrounds them and lies between them and the mesogloea. 

 I have had no means of ascertaining what is the precise chemical nature of this 

 substance, but it is undoubtedly of a horny consistency. It stains deeply in borax 

 carmine, and can be readily distinguished from the true mesogloea which lies below it. 

 It is a point of some importance, in comparing this genus with Cornularia, that in 



