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



Section I. SCLERAXONIA. 



Psevdaxonia, v. Koch, Morph. Jahrb., Bd. iv. p. 474. 



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

 by a canaliferous coenenchyma, 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 different in form from those of 

 the cortex. They are generally tightly packed, sometimes they 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 differentiated 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 Sympodiuvi and CaUipodiiim. There is still to 

 be found a more or less flatly expanded colony, in which the coenenchyma is divisible 

 into a firmer medullary and a softer cortical portion, but instead of clinging to a 

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

 fonning a branched tree-like colony as in Solenocaulon, Gray, and Leucoella, Gray. 

 AVitu 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 CoralUum. 



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

 Pseudaxonia 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 Melithaeacea. 

 The Briareacea he refers in part to the Alcyoninse. 

 The Scleraxonia include the following families : — 



I. Briareidse. 

 II. Scleroororoidse. 



& 



III. Melitodidse. 



IV. Corallidaj. 



' Skelet d. Alcyonarien, Morph. Jahrb., Bd. iv. p. 474, &c. 



