310 THE VOYAGE OF H.M.S CHALLENGER. 



hardly be regarded as certain— it would represent, to judge from the peculiarity of 

 the isolated spicules, a new species differing at once from Ai^hrocallistes bocagei and 

 Aphrocallistes beatrix. 



According to the report of Milne-Edwards,'' Aphrocallistes bocagei was also dredged 

 by the French " Travailleur" Expedition in the Atlantic Ocean, off the coasts of France 

 and Portu(!;al. 



After Zittel, in his Studies on the Hexactinellida," had mentioned that in the living 

 species of Aphrocallistes a very delicate framework extended over the outer surface and 

 the branches of the canals, Weltner described^ (1882) a continuous covering both on the 

 inner side and outer side of Ajjhrocallistes bocagei. In the case of the outer surface 

 he noted the presence of a delicate covering with large inhalent pores, which passed 

 into the characteristic parietal meshes and also spread over the ostia on the inner surface. 

 The outer membrane contained hexradiate spicules with an externally projecting fir-tree- 

 like ray and forming a regular mesh work; in the inner lay " the characteristic Aphrocallistes 

 rosettes, the rod-like spicule (thorn spicule), and the greatly reduced form which, though 

 only exhibiting four medium knobs, was yet recognisable as hexradiate, and lastly, 

 a large well-developed hexradiate form which is often fused to the parietal skeleton." 

 Moreover Weltner observed in his specimen " a third plasma layer between these 

 coverings of the outer and inner surfaces in the interior of the meshes (canals). This 

 was for the most part well preserved and was interrupted only in tlie middle, while it 

 was continued inwards to form an outer covering for the cavity of the sponge. In it the 

 free spicules of the internal covering were but seldom met with, although it stood in 

 manifold connection with the latter by means of plasma-threads. This third layer," 

 continues Weltner, " may indeed be an artificial product. I would not, however, leave it 

 unnoticed merely on that account, because it seemed to me to show that the free spicules 

 (flesh spicule) do not as a rule extend into the interior of the plasma." 



Character of the Genus. — The wall of the cup- or tube-like body is supported 

 by the honeycomb-like framework of the dictyonal skeleton. The radial canals which 

 traverse it, and are from 1 to 2 mm. in breadth, appear almost regularly hexa- 

 gonal and prismatic. The septa between the latter form a network of beams, with 

 irregular but predominantly three-sided meshes, from the margins and surfaces of which 

 conical pegs project, which are sometimes swollen and knob-like at their extremities. 

 Where three such bounding plates meet laterally the networks of beams usually fotnl 

 three-sided prismatic interspaces, and thus the margins of the six-sided prismatic canals 

 or honeycomb-like mesh-spaces become somewhat truncate or rounded. 



The strongly developed reticulate dermal membrane is continued without inter- 



1 Comptes rendus, 1881, vol. xciii. pp. 876-931 ; Ann. and Mag. Nat. Hist., vol. is. p. 46. 



» Ahlmndl. d. haier. Alcad., 1877, p. 49. 



3 Zur Kenntniss der Spongien, 1882, p. 32. 



