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



Section I. SCLERAXONIA. 

 Pseiidaxonia, v. Koch, Morph. Jabi-b., Bd. iv. p. 474. 



Fixed, upright, brauclied polyp-colonies ; the short iiolyp-tubes are surrounded 

 by a canaliferous ccenenchyma, in which numerous spicules are embedded. The axis 

 consists of a cortical substance in which the polyps are placed, and a medullary 

 substance. The latter contains spicules which are difterent in form from those of 

 the cortex. They are generally tightly packed, sometimes tliey are fastened together 

 by a horny substance, or even cemented into a strong axis by calcareous material. 

 In this, however, the individual spicules have always served as the basis. 



The section Scleraxonia is here regarded as a distinct division of the Gorgonacea, since 

 the component families exhibit a close mutual relationship, and diverge in many respects 

 from those of the Holaxonia. The axis, where such a supporting structure occurs, as 

 in the Holaxonia, is always composed of difterentiated spicules, which preserve a certain 

 independence even when the axis appears to the unassisted vision as a hard amorphous 

 mass. The variable consistence of the axis is due to the fact that the spicules may either 

 lie loosely together, or be united by a horny substance, or be bound together into a more 

 or less calcareous mass. The lowest forms of the Scleraxonia, such as occur among 

 the Briareidse, are closely connected to Sympodium and Callipodium. There is still to 

 Ije found a more or less flatly expanded colony, in which the ccenenchyma is divisible 

 into a firmer medullary and a softer cortical poi-tiou, but instead of clinging to a 

 substratum, as in the above mentioned forms of Cornulariidfe, the colony rises upright, 

 forming a branched tree-like colony as in Solenocaidon, Gray, and LeucoeUa, Gray. 

 With further differentiation the medullary mass comes to lie within a cylindrical stem, 

 and thus forms a central axis, which may be more or less specialised, and attains its 

 ■ highest development in Corallmm. 



The section of the Scleraxonia corresponds in great measure with the family 

 Pseudaxouia of v. Koch,' which this author regards as exhibiting a quite different mode 

 of axis-formation from that of his Axifera. 



Von Koch's Pseudaxonia includes the Corallinacea, Sclerogorgiacea, and Melith^acea. 

 The Briareacea he i-efers in part to the Alcyoninae. 

 The Sclera.xonia include the following families : — 



I. Briareidse, 

 )r^ 



1 Skelet d. ilcyoiiarien, Morph. Jahrh., Bd. iv. p. 474, i- 



II. Sclerogorgidse. 



III. Melitodidas. 



IV. Corallidas. 



