1900.] MARINE FAUNA OF CHRISTMAS ISLAND. 133 



in breadth and height. The surface is level, but shows a faintly- 

 marked tessellated pattern. The cortex is 2 mm. thick, and is 

 uniformly and densely crowded with spherasters. 



The spicule-measurements are given along with those of the type 

 specimen from Fremantle for comparison. 



Clioanosomal 

 Strongyloxea. Spherasters. oxyasters. Chiasters. 



Christmas Island.. 1 360 x 24 A i 70^ 18-24 fi 12 M 



Fremantle 1470 x 35 h i 70 /x 36 p 12 M 



Tethya inc/alli shows a considerable range of variation, but, I 

 think, would include the Christmas Island specimen in spite of its 

 oval form and the smaller size of its spicules. 



Distribution. Seychelles ; Australia ; Christmas Island ; Java ; 

 Amboina. 



Tethya seychellensis (E. P. Wright). 



1881. Alemo seychellensis E. P. Wright (19. p. 13, pi. i.) 



1888. Tethya seychellensis Sollas (17. p. 427, pi. xliv. figs. 1-6). 



There are five small, free, nearly spherical specimens, all of which 

 are gemmiferous. The outer two-thirds of the cortex is occupied by 

 a zone of subcortical cavities. 



Spicules. Megascleres — strongyloxea, 1200 x 18^. 



Microscleres — spherasters, 48 /u. Somal chiasters, 12 fi. Choano- 

 somal asters, 30 /*, with well-defined centrum ; actines roughened, 

 bifurcate. 



The " regular hexaster " type of the oxyasters is a characteristic 

 of this species, distinguishing it from T. ingcdli Bowerbank. 



A comparative table of spicule-measurements (in microns) of 

 specimens from various localities is given below. 



Strongyloxea 



Spherasters 



Somal chiasters . 



Choanosomal asters .. 



Distribution. Seychelles ; Philippine Islands ; Torres Straits ; 

 Christmas Island. 



Tethya affinis, sp. n. (Plate XII. fig. 1 ; Plate XIII. figs. 3a-d.) 

 Sponge incrusting, and of irregularly conical shape; upper 

 surface rough but level, with an obscure polygonal pattern formed 

 by depressed conules with fimbriated edges, and with two small 

 membranous oscular cones, the apertures being 1x5 mm. in 

 area. 



Cortex 1-22 mm. in thickness, with a few narrow intercortical 

 cavities arranged vertically in the outer two- thirds, the cortical 

 spherasters occasionally occupying the whole thickness but usually 



