SPONGES. 157 



The breaking up of the cortex into polygonal plates or nodules by pore-bearing 

 (and '. vent-bearing) grooves remind one forcibly of the genus Placospongia amongst 

 Spirastrellidse, but the resemblance is entirely superficial. 



Acanthoxifer ceylonensis. n. sp. Plate IX., fig. 5. 



Sponge massively encrusting, irregular, with flattened or convex upper surface and 

 broad base of attachment. Surface very minutely hispid or granular, uneven, nodular 

 or tubercular, the nodules or tubercles being very low and roundedly polygonal in 

 shape, separated by grooves of varying distinctness. Generally the grooves are broad 

 and shallow; sometimes they are narrow, with prominent margins. Diameter of 

 nodules, say, about 4 millims., but variable and irregular. Colour (in spirit) light 

 brown. Texture compact, fleshy, but with much calcareous debris embedded. Pores 

 and vents not recognisable externally. The largest specimen is cake-shaped, about 

 42 millims. in horizontal diameter, and up to 17 millims. in thickness. 



The main skeleton is a quite confused, lax reticulation of very abundant, long, oxeote 

 megascleres, occasionally collected together into loose, ill-defined bands, but without 

 any distinct fibre, and with a little spongin becoming visible in stained sections. The 

 cortical skeleton is very strongly developed and consists of dense brushes of oxea 

 placed side by side and lying at right angles to the surface, beyond which their apices 

 project (but are now nearly all broken off). These brushes are backed up internally 

 by a very dense, irregular reticulation of oxea. The cortical skeleton is absent 

 beneath the grooves which separate the surface nodules. Thus there is a separate 

 section of the cortical skeleton for each nodule or tubercle, thinning out as it 

 approaches the grooves in such a manner as to become strongly convex on the inner 

 aspect. 



Spicule*. (I.) Smooth oxea (Plate IX., fig. 5, a) ; long and rather slender, slightly 

 curved or bent, variously and often irregularly ended, sometimes stylote (Plate IX., 

 fig. 5, J>). Size variable, say about 0'74 millim. by 0"012 millim. Abundant in the 

 main skeleton and occasionally met with in the surface brushes. 



(2.) Spined oxea (Plate IX., fig. 5, c) ; usually slightly and symmetrically curved 

 (or angulated) in the middle ; tapering fairly gradually to a sharp point at each end ; 

 provided with numerous very minute, sharp spines, most abundantly developed 

 towards the two ends; size about 0'38 millim. by 0'008 millim. Characteristic of the 

 cortical skeleton, but also common in the interior of the sponge. 



(3.) Trichodragmata (Plate IX., rig. 5, d) ; oblong bundles of extremely slender 

 rhaphides, which do not usually become dissociated even on boiling with nitric acid. 

 Size usually about O'Olfi millim. by 0'004 millim. : occasionally much longer. 



Stained sections show that the ectosome (between the spicules) is chiefly collenchy- 

 matous, sometimes with a tendency to become fibrous near the surface. In both 

 ectosome and choanosome are an immense number of minute granules of a pale 



