138 CEYLON PEAEL OYSTER REPORT. 



Surface smooth, but rather uneven. Vents numerous and conspicuous, circular, from 

 about 1 millim. to 2 - 5 millims. in diameter; mostly flush with the surface, hut 

 occasionally on low prominences. Colour (dry) dull greyish-brown, with a purplish 

 timre in places, which seems to indicate that it was purple in life. Texture (dry) 

 compressible and resilient, but rather stiff. 



The main skeleton is a rectangular-meshed network of horny fibre cored by spicules, 

 in which the meshes vary greatly in size. The principal fibres are about 0'033 millim. 

 in diameter, and contain a multispicular core of small oxea which occupy only about 

 one-third (or less) of the total thickness of the fibre. The secondary fibres are more 

 slender and contain fewer spicules. The dermal skeleton (Plate IX., fig. G) is, for the 

 most part, a unispicular reticulation of oxea with comparatively little spongin ; some- 

 times one sees brushes of projecting oxea, but I am not sure how for these are proper 

 to the dermal skeleton. 



Spicules. (1.) Oxea (Plate IX., fig. 6, o) ; short, slender, slightly curved, sub- 

 fusiform, gradually and sharply pointed at each end ; size about - l millim. by 

 0'004 millim. A number of very slender, hair-like oxea, probably young or vestigial 

 forms, also occur. 



(2.) Sigmata (Plate IX, fig. 6, s) ; very slender and hair-like, C-shaped, up to 

 about - 02 millim. from bend to bend. Abundant. 



This species is nearly related to Gellioden licheniformis (Lamarck),'" but differs, at 

 any rate from the " Challenger" specimen of that species, both in external form and 

 in the much smaller size of the spicules and more regular arrangement of the 

 skeleton. 



R.N. 1 12 (Gulf of Manaar, dry). 



Gelliodes petrosioides, n. sp. Plate IX., fig. 3. 



Sponge massive, depressed, cushion-shaped ; flattened below, where it has appa- 

 rently been attached by a broad base ; evenly rounded oft' and strongly convex above. 

 Surface coarsely granular, not hispid. Vents not visible. Pores numerous, scattered 

 in the thin dermal membrane which roofs over the numerous small, rounded sub- 

 dermal cavities. Colour (in spirit) pale yellowish-grey. Texture compact ; hard and 

 almost stony. Greatest diameter of specimen, which is irregularly rounded in outline, 

 about 24 millims. 



The main skeleton is a very dense but quite irregular reticulation of very coarse, 

 stout, densely spicular fibre, with a great many loose megascleres scattered between. 

 The stout fibres have a thickness of about (P164 millim., and probably contain a 

 certain amount of spongin, which, however, is not visible in ordinary sections. The 

 dermal skeleton cannot he sharply distinguished from the main skeleton, and consists 

 of an irregular reticulation of coarse spicular fibre, the interspaces in which are 

 occupied by the thin, pore-hearing dermal membrane. 



* Vide Riih.f.y and Dendy, ' "Challenger" Mon.axoirida,' p. 48. 



