1900.] MAEINB EATJITA 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. 



Choanosomal 

 Strongyloxea. Spherasters. oxyasters. Ckiasters. 



Christmas Island . . 1360 x 2-1 /j. 70 li 18-2-1 li \2li 



Fremantle 1470 x 35 li 70 li 36 li V2li 



Teihya ingalli 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. 



Tethta seychellexsis (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 lSyu. 



Microseleres — spherasters, 4$ p. Somal chiasters, 12 li. Choano- 

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

 bifurcate. 



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

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



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

 specimens from various localities is given below. 



Type from Samboangan. Torres Straits. Christinas 

 Seychelles. 'Challenger.' 'Challenger.' Island. 



Strongyloxea 1750x30 1910x23 1680x26 1200x18 



Spherasters 70 95 64 48 



Somal chiasters 12 12 12 12 



Choanosomal asters ... 54 60 60 30 



Distribution. Seychelles ; Philippine Islands ; Torres Straits ; 

 Christmas Island. 



Tethya affixis, 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 



