49(5 MR. S. O. RIDLEY ON SOME 



Echinodictytjm nervosum. (Plate XXVIII. figs. 7-10.) 



Spongia nervosa, Lamarck ?, Ann. Mus. Hist. Nat. Paris, xx. p. 450 ; 

 Anim. s. Vert. (2) ii. p. 567- 



Spongia cancellata, Lamarck?, Ann. Mus. Hist. Nat. Paris, xx. p. 456 ; 

 Anim. s. Vert. (2) ii. p. 571. 



Sponge branched in one plane from almost obsolete stem ; 

 brandies long, anastomosing at points, which are generally adjacent 

 in the various branches; near base irregularly cylindrical, becoming 

 flattened higher up ; apices digitiform, adjacent edges narrow, 

 knife-like. Surface normally covered by dense white incrustation ; 

 minutely reticulate on back, aud minutely hispid in front of frond 

 when this is removed. Texture bardish ; it is slightly elastic, but 

 easily broken. Colour in dried state pale yellowish white. 



Vents numerous, in one side only of frond (the front), scattered, 

 numerous, 1 to 2 mm. in diameter, indistinctly defined. Pores ? 



Main skeleton composed of spiculo-fibre, in which the smooth 

 acerate spicules almost entirely conceal the ceratinous uniting 

 substance ; primary fibres straight, at right angles to surface, from 

 3 to 6 spicules in diameter ; secondary fibres short, about 1 spi- 

 cule long and 2 to 3 broad, connecting primaries at various angles ; 

 both sets of fibres sparsely echinated by single, short, entirely - 

 spined cylindrical spicules. 



Dermal skeleton consisting of broad, irregularly anastomosing 

 tracts of smooth acuate spicules slightly echinated by spined 

 spicules. 



Sarcode transparent. Ceratinous material amber-yellow in 

 basal skeleton, almost colourless in branches ; polarizes light. 



Skeleton-spicules of one kind : — Smooth stout acerate, bent at 

 a slight angle, and tapering to sharp points from about the centre 

 (as occasional variations they may have one or both ends rounded 

 off) ; size '39 (occasionally *46) by -03107 (occasionally -038) mm. 



Ecliinating spicule short, straight, spined, cylindrical, tapering 

 slightly from rounded base (which is slightly inflated in some 

 cases) to distal rounded end ; spines abundant, strong, and recur - 

 vate over distal half, slighter and curved towards apex on base, 

 very slight or absent on part immediately above the base ; size 

 •114 by -0174 mm. 



Hal. S.E. coast of Arabia (Carter) (Indian Ocean ?, Lamarck). 



Examined. Dry and mounted in balsam. 



Obs. The dry specimen in the Bowerbank collection is 9 inches 

 high, and about the same in breadth at the broadest part. 



Another species of this genus is known to me, to which I hope 

 to refer on some future occasion. 



