TETRAXONIDA 293 



them all in external form. The specimen is massively flabellate, 12 cm. high, 14 cm. 

 across and 2 cm. thick. 



Genus Biemna, Gray 



Biemna chilensis, Thiele. 



B. chilensis, Thiele, 1905, p. 434, fig. 54; B. macrorhaphis, Hentschel, 1914, p. 74, pi. vi, fig. 3. 



Occurrence. St. 177 : South Shetlands, 1080 m. ; St. 187 : Palmer Archipelago, 259 m. ; St. WS 243 : 

 Falkland Islands, 144-141 m. 



Distribution. Calbuco, Chile ; Wilhelm Land. 



Genus Asbestopluma, Norman 



Asbestopluma calyx, Hentschel. 



A. calyx, Hentschel, 1914, p. 66, pi. iv, fig. 4, pi. v, fig. 11. 

 Occurrence. St. 156: South Georgia, 200-236 m. 

 Distribution. Wilhelm Land. 



Genus Arenochalina, Lendenfeld 



The genus, established by Lendenfeld (1887, p. 821) for a single species A. mirabilis, 

 possesses very slender subtylostyli, not oxea as originally stated, and according to 

 Hallmann (1912, p. 252 footnote), possibly anisochelae. There are several specimens in 

 the British Museum collection, identified by Lendenfeld, which if not actual type speci- 

 mens are sufficiently representative of the species to serve in their stead. From these it 

 is obvious that the species is a degenerate Mycale. 



The second species which I propose to assign to the genus differs from the type 

 species in the structure of the skeleton, but agrees in the shape of its megascleres. The 

 two may possibly be unrelated, but they are sufficiently alike in some features to make 

 it convenient to include them provisionally in the same genus, and the diagnosis is 

 emended accordingly. 



Diagnosis. Reduced Mycaleae with main skeleton composed of very slender sub- 

 tylostyli, having enlarged axial canals; skeleton either a sub-isodictyal network of 

 spongin fibres cored by spicules, or composed of loose wisps of spicules running 

 vertically to surface and branching and anastomosing en route ; special dermal skeleton 

 absent; microscleres, when present, palmate anisochelae, toxa or both. 



Arenochalina incrustans, sp.n. (Fig. 19). 



Hohtype. B.M. 28. 2. 15. 360. 



Occurrence. St. 2: Ascension Island, attached to buoy. 



Diagnosis. Sponge encrusting ; surface smooth, slightly conulose ; oscules and pores 

 not visible; colour, in spirit, white; skeleton composed of wisps of spicules running 

 more or less vertically to surface, branching and anastomosing as they go; outermost 



