SPONGES — WHITELEGGE. 477 



DESMACIDON STELLIGERA, sp. nov. 



(Plate xliv., fig. 11.) 



Station 53. 



Sponge flabellate, about 270 mm. high, 130 mm. broad, and 

 from 5 to 10 mm. in thickness. The frond is divided into two 

 portions ; the larger is lanceolate and lobate on the margins, 

 especially near the summit ; the smaller portion is ligulate and 

 about 35 mm. wide. Both originate from a slightly thickened 

 and highly conulose stem about 30 or 40 mm. in diameter and 

 30 mm. high. The base of attachment is flat and well defined, 

 but not enlarged. The surface pi^esents in the depressions a 

 smooth non-porous dermis, but where this is eroded it is closely 

 covered with more or less oblong pores about 0'5 mm. in width 

 and 1 or 2 mm. in length ; they have a tendency to become 

 radiate, and give the surface an appearance quite peculiar and 

 characteristic of the species. The elevations vary from 2 to 

 8 mm. in height, and consist of a series of oscula openings in 

 groups of three or more. The latter are surrounded by numerous 

 radiating grooves which extend to a distance of 10 mm. or more 

 from the central oscular bearing elevations, some of which on the 

 unabraded parts are covered with membrane, and it appears 

 probable that this would be valvular in its action and to some 

 extent regulate both the inflow and outflow of water. Texture 

 hard and tough, scarcely compressible between the fingers. 

 Colour dull yellowish-grey. 



Skeleton consisting of a complicated network of stout fibres 

 with usually a more or less rounded mesh. The main fibres are 

 enveloped in a fair amount of spongin, and their diameter is 

 usually about 0-25 to 0-3 mm. The core consists of a dense 

 mass of chiefly broken spicule fragments, probably of 

 foreign origin ; the latter appear to be ensheathed with proper 

 oxeote spicules, many of which are embedded in the fibres by 

 their basal third and stand out nearly at right angles to the 

 fibre, so as to appear as echinating spicules ; their oxeote form, 

 however, appears to preclude such being the case. The second- 

 aries are 0-1 mm. in diameter and consist of closely packed oxea ; 

 the connecting fibres are composed of a few diffuse spicules, and 

 rarely exceed 0'5 mm. in diameter. 



Megascleres : — straight or but slightly fusiform oxea with 

 moderately sharp points. Size in the fibres 0-17 by 0-001 mm.; 

 the dermal spicules are somewhat shorter and a little stouter. 



Microscleres : — sigmata both simple and contort. Size from 

 0-05 to 0-07 mm. long. 



