1900.] MARINE FAUNA OF CHRISTMAS 1SLASD. 139 



Spicules. Strongyles 126x8/*, slightly curved in the middle. 

 Oxea 108 x 2*5 p, curved at the centre ; also very slender oxea of 

 the same length and shape, probably young forms of the thicker 

 kind. 



The specimen encrusts a Melina-sheW, and is produced at one 

 point into a short, stout, digitate process. 



There is in the British Museum Collection an unnamed specimen 

 (registered 82.10.17.246) of this species from Marie Louise Island, 

 Amirante Group. 



The species from Providence Island described by Ridlev (11. 

 p. 607, pi. liv. fig. ?') as " Reniera sp. allied to crateriformis " has 

 spicules of the same shape, but much larger (480 X 28 /x), and the 

 meshes of the reticulum are multispiculate. 



Distribution. Amirante Isles ; Christmas Island. 



Pjetrosia exigua, sp. n. (Plate XII. fig. 7 ; Plate XIII. fig. 4.) 



Sponge forming a hard, thick, nodulated crust. Colour pale 

 grey; surface smooth, and in parts showing an irregular reticulate 

 pattern formed by pore-areas. 



Oscules 1 to 1*5 mm. in diameter, numerous, some level with 

 surface, others with slightly raised margin. 



Skeleton formed of slender main lines of fibres passing verti- 

 cally to the surface and connected at right angles to this plane 

 by closely packed single spicules, so as to form circular or obscurely 

 polygonal tubes about 70 mm. in diameter, the skeletal tubes being 

 much more apparent near the surface and very ill-defined deeper, 

 where the skeleton becomes a dense, confused network. Special 

 dermal skeleton absent. 



Spicules. Oxea 114x5 - 5/i, curved at the centre, and dimin- 

 ishing to very sharp points. 



The single specimen is 4 x 4 c.c. in area, and 1*5 c.c. in thickness, 



The salient character of this species lies in the very small size of 

 the spicules, which are less than half the size of those of Petrosia 

 similis Ridley & Dendy (13. p. 9, pi. ii. fig. 10, pi. iii. figs. 3 & 4), 

 a species closely allied to it in other respects ; the spicules are 

 considerably smaller than those of any species with oxeote spicules 

 from this region of the Indo -Pacific. 



HAiiicnoNDEiA solida Ridley & Dendy. 



1886-7. Haliohondria solida Ridley & Dendy (12. p. 326, and 

 13. p. 4, pi. ii. fig. 5). 



The specimen, which is white and with an even surface, differs 

 slightly from the type in having the ends ot the oxea sharp-pointed ; 

 the spicules (770 x 22 jj) are curved at the centre. 



Distribution. Amboina ; Tahiti; Christmas Island. 



Halichonjdria solida var. rugosa Ridley & Dendy. 



The specimen is dark brown and wrinkled in places, as in the 

 type of the variety from Api. There are several oscnles, from 1 to 

 4 mm. across, with conspicuous membranous sphincters. The 



