TETRAXONIDA 



321 





Remarks. The genus, with its extremely simple skeleton, is not easy to classify. The 

 presence of acanthostrongyla suggests at once an affinity with the Ectyoninae, and, for 

 the time being at all events, I propose to regard it as a primitive Ectyonine, preferably 

 as one of the Clathrieae. 



Protoclathria simplicissima, sp.n. (Plate LVI, fig. 2; Fig. 31). 

 Holotype. B.jVI. 28. 2. 15. 369. 

 Occurrence. St. 6: Tristan da Cunha, 80-140 m. 



Diagnosis. Sponge pyriform or massive, irregular; surface 

 even, hispid; oscules and pores not apparent; texture firm but 

 friable; colour, in spirit, dark grey; skeleton sub-isodictyal, con- 

 sisting of a densely knit triangular mesh, usually multispicular but 

 often unispicular in patches; no special dermal skeleton; little or 

 no spongin; microscleres of two kinds only, tylostyli and acan- 

 thostrongyla; tylostyli, forming bulk of skeleton, usually curved 

 or even strongly angulated at or near the centre, often reduced to 

 styli or, more rarely, to oxea, 0-26 by 0-015 mm. ; acanthostrongyla, 

 of very rare occurrence, not echinating the skeleton but occupying 

 same relative position as tylostyh, straight, o-i8 by 0-012 mm. 



Remarks. In deciding the systematic position of this species, 

 the difficulty is increased by the distribution of the acanthostrongyla. 

 In the holotype they are numerous; in the first co-type they are 

 rare; and in the third specimen they appear to be absent altogether. Fig.^i.Protoclat/i- 

 In the last therefore the skeleton consists only of tylostyli, and the "" '''"Pl'''"'"'"' 



• I 11 1 1 , r, , sp.n. a, substylo- 



sponge might well have been placed among the Suberitidae had it style; h, acantho- 



not been possible to make a comparison with the first two specimens. style. > 320. 



u 



b 



Genus Ophlitaspongia, Bowerbank 



Ophlitaspongia membranacea, Thiele. 



O. membranacea, Thiele, 1905, p. 450, figs. 67, 105. 



Occurrence. St. 152: South Georgia, 245 m. 



Remarks. The two specimens show a marked resemblance to the holotype of O. mem- 

 branacea, Thiele, in the shape and disposition of the spicules, but differ in the external 

 form and in the dimensions of the spicules. The first specimen consists of an erect 

 digitate lobe bearing a small lateral branch, while the second is massive with incipient 

 digitate processes at the top. Both have, however, a strongly hirsute surface as in the 

 holotype. In the second specimen the smaller megascleres measure 0-5 by 0-024 rn"^- 

 and the larger 1-2 by 0-036 mm. The auxiliary subtylostyli ("diinnen Style" of Thiele, 

 he. cit., p. 45 1 ) measure 0-3 by 0-003 mm. In the first specimen, the dimensions of these 

 spicules are much the same except that the larger megascleres often attain a length of 



