626 COLLECTIONS FROM THE WESTERN INDIAN OCEAN. 



50. Erylus cylindrigerus *. 

 (Plate LIH. fig. M; Plate LIV. figs, e-e""".) 



Massive, suberect ; terminating above in a lobate prolongation. 

 Surface smooth, slightly uneven. Vents one (or more ?) near apex 

 of sponge, about 2 millim. in diameter, opening flush with surface, 

 leading obliquely and deeply downwards into sponge. Texture in 

 spirit tough, firm, but somewhat flexible ; colour in spirit dark 

 brown, almost black. Skeleton composed of bundles of spicule 

 no. 1, 6-8 spicules broad, radiating from centre to just below sur- 

 face, '17 to -3 millim. apart near surface. Surface covered with a 

 layer about '1 millim. thick of the discoid spicule no. 2, arranged 

 horizontally. Sarcode subtransparent, very pale brown, almost 

 colourless. 



Spicules: — (1) Zone-spicules subcyliudrical, smooth, straight or 

 very slightly and gradually curved, tapering from within about six 

 diameters of ends to rounded terminations of about one third the 

 diameter of the middle of the shaft ; size about '7 by -032 millim. 

 (2) Discoid, of subdiamond-shaped outline, viz. that of a rhombus 

 with the angles rounded off; length '21 to -28 millim., breadth 

 •1 to '14 millim., thickness about "04 millim. ; covered with minute 

 low punctiform spines, about '012 millim. apart (spines, as seen 

 under a high power from above, stellate in outline ; they are multifid 

 terminally). (3) Acerate, smooth, slightly and gradually curved, 

 tapering to sharp points from centre ; size '06 by '0032 millim. 

 (scattered abundantly throughout sarcode). (4) Stellate, with about 

 10-12 straight rays -003 millim. thick at base, tapering to sharp 

 points, springing from a slight central body -01 to '013 millim. in 

 diameter ; expanse of spicule about '05 millim. (5) Stellate like 

 the preceding, but arms about 16 in number and expanse about 

 •02 millim. 



Bab. Providence Eeef, Mascarene group, 24 fms. ; bottom, sand 

 and dead coral. 



A single specimen with a somewhat spreading base, which encloses 

 calcareous fragments, rising into a subcylindrical, terminally rounded, 

 finger-like column, 30 millim. high and 12 millim. in mean 

 diameter, slightly overgrown by a delicate Sertularian Hydroid ; 

 extreme diameter of base 40 millim. 



The species is most closely allied to Stelletta euastrum, Schmidt, 

 from Algiers, and to forms so named by Carter (Ann. & Mag. N". H. 

 1880, v. pp. 135, 136) from Ceylon and Australia, which perhaps 

 represent another species. Instead of the trifid zone-spicule with 

 bifurcate arms found in Schmidt's species, it has simply a subcylin- 

 drical spicule, usually blunt at both ends, and wants the long 

 slender acerate ; the few-armed stellate has its arms more numerous 

 (10-12 instead of 2-4, which is the range represented by Schmidt's 



* From the cylindrical zone-spicule. 





