REPORT ON THE MONAXONIDA. 81 



the branches terminate in a thick, fleshy lamella, of which there appear to be usually six 

 or seven in a full-grown example, increasing gradually in size from below upwards. 

 Each lamella has the form of a deeply concave, transversely elongated cup. The concave 

 surface is directed towards the stem (posterior) while the convex surface is anterior, and 

 the supporting branch, or peduncle, is inserted into the centre of the lower margin of each 

 lamella ; sometimes the weight of the large upper lamellse causes the stem to di-oop 

 considerably, and the lamellse to hang down with their concave surfaces uppermost. 



There are in the collection thirteen specimens, the stem of the smallest (PI. XVIII. 

 fig. 3) being only 38 mm. high, and bearing two rounded, cup-shaped lamellse about 

 13 mm. in diameter. The foUowiug are the measurements of a very fine and 

 apparently full-grown specimen, with six cup-shaped lamellae. Diameter of expanded 

 base 19 mm., thickness of same 8 mm. Height of stem, from the point where it 

 rises out of the expanded base to its insertion into the margin of the uppermost cup- 

 shaped lamella, 200 mm.; longer diameter of stem, at a point half way between the 

 origins of the third and fourth branches, about 8 mm.; diameter at right angles to the 

 above about 3 mm. Longest diameter of the uppermost lamella, 63 mm.; diameter 

 at right angles to the above, 35 mm.; thickness of same, about 4 mm. Colour in 

 spirit light yellow. Texture, of the stem, very dense and tough ; of the lamella, rather 

 soft and fragUe, but firm. Surface of the stem markedly hispid. Concave surface 

 of lamellse slightly glabrous in appearance, but really very minutely hispid ; convex 

 surface, minutely hispid ; both, as a rule, evenly rounded. Dermal membrane obvious 

 only on the concave surface, where it is distinct, thin and very transparent. Oscula 

 confined to the convex surfaces of the lamellse, over which they are thickly and evenly 

 scattered, small (averaging little over 0*5 mm. in diameter), round, and having their 

 margins flush with the general surface of the sponge. Pores confined to the concave 

 surfaces of the lamellse, where they are enormously abundant, reducing the dermal 

 membrane to a mere network (PI. XVIII. fig. 4) ; they are almost circular openings 

 and of very uniform size, averaging about 0"11 mm. in diameter. Indications are not 

 wanting that these " pores " were, in the living condition, broken up into still smaller 

 openings by bands of delicate membrane, but on this point we are not certain. 



Skeleton. — (1) The skeleton of the stem; this consists simply of a dense core of 

 closely packed stylote spicules, for the most part placed longitudinally, but with numerous 

 spicules projecting at right angles, and thus giving to the stem its hispid character. 

 (2) The skeleton of the lamellse. (a) Dermal; supporting the dermal membrane on the 

 concave surface is a fairly regular reticulation of rather stout spiculo-fibre, from which 

 numerous spicules project outwards and thus give to the surface its hispid character ; this 

 reticulation is absent from the convex surface, (b) Main; each branch breaks up, at 

 the point where it enters the lamella, into a number of radiating fibres, arranged in a 

 fan-like manner, and in addition to the skeleton thus constituted there is a Halichon- 



(ZOOL, CHALL. EXP, — PAET LIX. — 1887.) Nllll 11 



