310 DISCOVERY REPORTS 



arrangement of skeleton and external form, and (2) the changes which accompany 

 maturity. 



The variation in the external form is not considerable and the present specimens agree 

 closely in this, and in the texture, with the holotype. The form ranges from irregularly 

 massive to sub-spherical or flabellate. The surface may be minutely conulose or thrown 

 into conspicuous rounded tubercles. The largest flabellate specimen measures 9 cm. 

 high, by 9 cm. across, by 4 cm. thick. The largest sub-spherical specimen is 7 cm. in 

 diameter. The smallest is sub-spherical and i cm. in diameter. 



The skeleton varies between regularly isodictyal, with polyspicular primary fibres 

 joined at intervals by horizontally arranged single spicules, and sub-isodictyal, with 

 triangular meshes. 



Distribution. Graham Land; Wilhelm Land; Victoria Land; east coast of South 

 America up to mouth of Rio de la Plata. 



Myxilla australis (Topsent) (Plate LIV, fig. 6). 



Detidoryx incrustans, var. australis, Topsent, 1901, p. 7; id., 1901, p. 17, pi. iii, fig. 11 ; Myxilla 

 australis, id., 1917, p. 53, pi. vi, fig. 10. 



Occurrence. St. 190: Palmer Archipelago, 93-130 m.; St. WS 27: South Georgia, 106-109 ™^- 



Diagnosis. Sponge encrusting or massive; surface smooth, uneven, minutely reti- 

 culate; oscules large, conspicuous, leading into deep cloacal cavities; pores scattered 

 generally over surface ; dermal membrane readily separable, translucent, showing large 

 sub-dermal cavities beneath; colour, in spirit, white; main skeleton a sub-isodictyal 

 reticulation of spined styli ; dermal skeleton composed of numerous loose bundles of 

 tornota, set at right angles to surface, with outer ends supporting a tangential reticulation 

 of similar spicules; styli of main skeleton, sparingly spined throughout length, o-44-o-6 

 by 0-0 1 5-0-0 1 8 mm. ; tornota, usually in form of straight, slender styli, bearing scattered 

 spines at each end, o-27-o-35 by o-oo8-o-oi mm.; tridentate isochelae of two sizes, 

 larger o-047-o-o6 mm., and smaller 0-024 ^^- long; sigmata 0-03-0-06 mm. 



Remarks. The present specimen appears to agree closely with the holotype of the 

 species, except for the presence of the second type of chelae. Since these are small and 

 not numerous, it is possible that Topsent overlooked them in his original examinations. 



Distribution. Graham Land. 



Mj^illa asigmata, Topsent. 



M. spongiosa, var. asigmata, Topsent, 1901, p. 18; Lissodendoryx spongiosa, var. asigmata, id., 

 1908, p. 26, pi. iii, fig. I ; Myxilla spongiosa, var. asigmata, id., 1913, p. 625, pi. iii, fig. 3; 

 Hentschel, 1914, p. 99. 



Occurrence. St. 145: ofi" South Georgia, 26-35 m. 



Remarks. Of the specimens hitherto recorded the majority have been encrusting or 

 massive but spreading. That described by Topsent (1913) was, however, pyriform and 

 slightly pedunculate. In all the surface is slightly conulose. The present specimen 



