1900.] MARINE FAUNA OF CHRISTMAS ISLAND. 135 



The differences between the type specimen from Torres Straits 

 on the one hand, and the specimens from Amboina, Java, and 

 Christmas Island on the other, are constant, and render it necessary 

 to regard the latter specimens as belonging to a well marked 

 variety. In the type the tylostyles are longer and narrower, and 

 the largest spirasters are smaller than in the new variety which I 

 have named " robusta." 



Type. Var. robusta. 



Tylostyles 507 x 8 M 432 x 12 li 



„ head 12 li 12 li 



,, neck 6 li 10 /z 



Spirasters, smallest 8-12 ll 8-12 ii 



„ largest 36 ll 48 it 



Distribution of S. decumbens : Torres Straits ; of S. decumbens 

 var. robusta : Philippines, Java, Christmas Island, Bed Sea. 



Pseudosuberites andrewsi, sp. n. (Plate XII. figs. 2 a-b ; 

 Plate XIII. fig. 7.) 



Sponge loosely incrusting or forming free thick lamellae. Pale 

 yellow in colour ; surface smooth, and with canalicular markings 

 beneath the dermis ; soft in consistence and easily torn. Oscules, 

 when present, small, circular (-75 mm. in diameter), guarded by a 

 silvery fringe or conule of tylote spicules with points centripetal. 



Skeleton composed of primary lines of multispicular fibres 

 radiating to the surface and giving off at various angles a few 

 scattered single spicules. 



Dermal skeleton very distinct and formed of tangentially 

 arranged bundles of spicules joining to form a reticulum with tri- 

 or quadrangular meshes. 



Spicules. Tylotes 350 x 6 p, slightly curved in the basal third ; 

 head rounded, 7'5 *t in diameter, slightly knobbed at the summit 

 or swollen laterally. 



Of the three specimens, one is incrusting and with oscules, the 

 others are free and without oscules ; the former is 5*5 x 3 c.c. in 

 area, and -5 c.c. in thickness ; the latter are considerably thicker. 



The genus at present includes, as stated by Topsent, two other 

 species, P. hyalina (Ridley & Dendy) and P. sulphureus (Bower- 

 bank). One of the small fragments of the type specimen of 

 P. hyalina has an oscule with the palisade of spicules arranged 

 as in the new species, but the tylotes are much larger in the 

 former, measuring 1100 X 25 fx. 



Htmeniacidon conulosum (Topsent). 



1897. Stylotella conulosa Topsent (18. p. 466). 



1898. Hymeniacidon conulosum Lindgren (10. p. 313, pi. xvii. 

 fig. 13; pi. xix. hg. 19). 



The single specimen is pyramidal, 3 c.c. in height, and with an 

 incrusting base 3 xl'5 c.c. 



The surface is partly even, and partly provided with small 

 hispid tufts. 



