REPORT ON THE MONAXONIDA. 45 



these occur iu liis species, is shown b}'' a preparation in the Bowerbank collection in the 

 British Museum. Vosmaer, presumably following Bowerbank, also omits to mention the 

 sigmata. The discovery of these sigmata fully justifies the reference of this species to 

 the genus Gellius. 



The measurements of the spicules are as follows : — Oxea (megasclera) 0"29 to 0'34 

 by 0'009 to O'Ol mm. Toxa (microsclera) 0"08 by 0'0012 mm. Sigmata (microsclera) 

 0-019 by 0-0012 mm. 



Zoca%.— Station 75, July 2, 1873; lat. 38° 38' 0" N., long. 28° 28' 30" W. ; off 

 the Azores ; depth, 450 fathoms ; bottom, volcanic mud. Three small specimens. 



Habitat. — British Seas (Bowerbank) ; off Azores (Challenger). 



Gellms jlahelliformis, Ridley and Dendy (PI. XXVI. figs. 5, 5a). 



1886. Gelliits jlahelliformis, Ridley and Dendy, Ann. and Mag. Nat. Hist., ser. 4, vol. xviii. 



p. 334. 



Sponge (PI. XXVI. figs. 5, 5a) erect, compressed, forming thin laminae. The largest 

 piece forms an erect, flattened, broadly expanded lobe, arising from a small woody base and 

 rapidly expanding upwards; margin entire, thin, turned back; in addition to this back- 

 ward curvature of the margin, which would appear most plainly in longitudinal section, 

 the lameUa is also curved in a direction at right angles to the former, the second curvature 

 being most evident in horizontal section, and causing the sponge to become convex on 

 one side and concave on the other. The specimen, in fact, resembles a piece broken off 

 from a cup, with the lip turned back; it is not improbable that the sponge may some- 

 times be caliciform, but we do not think the present sjDecimen has ever been so. 

 Height of the largest piece 68 mm., greatest breadth 79 mm., thickness about 

 4 to S mm. Colour in spirit greyish-yellow. Texture very fragile. Surface even, 

 with a deeply, though minutely, pitted appearance all over. On the convex side each 

 little pit is covered over by the pore-bearing dermal membrane, but on the concave side 

 the pits seem to represent the oscula, for we have been able to find none other. Dermal 

 membrane very delicate indeed. Oscula (? minute, very abundant over the concave 

 surface). Pores, very numerous rounded openings iu the dermal membrane on the 

 convex surface, measuring about 0-085 mm. iu diameter, reducing the dermal membrane to 

 a mere network. We have found none on the concave surface, but should not like to say 

 for certain that they do not exist here, though proliably, from the analogy of other 

 flabellate sponges, they are almost or quite confined to the one surface. 



Skeleton. — (a) Dermal; there is no very definite dermal skeleton on either side of the 

 sponge, but on the pore-bearing side the toxa are enormously abundant and arranged 

 in loose, irregularly reticulating, fibre-like tracts. (Jj) Main; a loose and cpite irregular 

 reticulation of oxeote spicules. 



