TETRAXONIDA 



Hymeniacidon dubia, sp.n. (Plate LVI, fig. 9; Fig. 34). 



Holotype. B.M. 28. 2. 15. 364. 



Occurrence. St. WS 83: Falkland Islands, 137-129 m. 



Diagnosis. Sponge massive, clathrate ; surface minutely hispid and 

 beset with warty protuberances, as though sponge body were composed 

 of numerous thickly-set branches which had anastomosed, leaving 

 stunted ends exposed at surface; oscules not seen; skeleton a con- 

 fused reticulation of, usually, single spicules; spicules styli, usually 

 thickest at centre and tapering away at each end, 0-48 by o-ii mm. 



Remarks. The species approximates more closely to Axinella verru- 

 cosa, Br0ndsted, from New Zealand, than to any other species of 

 Axinellidae. It diff'ers from that species in the absence of spicule fibres 

 and of strongyla and in the size of the spicules. The most important 

 feature they have in common is that the styli are thickest at the centre 

 and thence taper gently towards each end, in the manner of the 

 megascleres of Polymastio, instead of having the same diameter 

 throughout their length except at the distal end where they taper to a 

 point, as in the typical Axinellid style. In all respects, however, the 

 present species is a typical Hymeiiiacidoyi. Further, many of the 

 spicules, smaller than the rest and probably only young forms, are 

 regularly stylote, as in the typical Axinellid. 



329 



Fig. 34. Hytnenia- 

 cidon dubia, sp.n. 

 Style, X 200. 



Genus Thieleia, gen.n. 

 Genotype. Hymeniacidon rubiginosa, Thiele. 



Diagnosis. Main skeleton composed of delicate strands of spicules running vertically 

 to the surface and connected to each other by irregularly arranged masses of single 

 spicules. At the surface, the ends of the strands diverge to form dense brushes of spicules 

 the apices of which project slightly beyond the dermis. There is no special dermal 

 skeleton, unless the dense brushes formed from the ends of the strands of the main 

 skeleton can be regarded as such. 



Thieleia rubiginosa (Thiele). 



Hymeniacidon rubiginosa, Thiele, 1905, p. 421, fig. 44. 

 Occurrence. St. 157: South Georgia, 970 m. 

 Distribution. Iquique. 



Analysis of the species of Hymeniacidon of the South Atlantic-Antarctic region 

 Of the numerous species hitherto assigned to the genus Hymeniacidon, the majority 

 have proved to be synonyms of H. caruncula and H. sanguinea, or are now known to 

 belong to other genera. Of the remainder, five are recorded from the South Atlantic- 

 Antarctic region. 



