SPONGES. 121 



gradually and more or less sharply pointed at the other ; size variahle, up to ahout 

 0'47 millim. by O'Ol millim. 



(2.) Spherasters; (a) comparatively large, with large centrum and stout, smooth, 

 conical, sharply pointed rays; closely resembling the large spherasters of Tethya ; 

 total diameter about 0'02 millim. ; (?>) of medium size, with moderately developed 

 centrum and stout, sub-cylindrical, very distinctly tylote rays (? heads sometimes 

 roughened), about as long as the diameter of the centrum ; total diameter of spicule 

 about 0-012 millim. ; (c) small, with very small centrum and comparatively long, 

 slender, sharp-pointed rays ; total diameter about 0*008 millim. (possibly young forms 

 of one or both of the others). 



R.N. 220B (deep water off Galle and onwards up West Coast of Ceylon). 



Hymedesmia curvistellifera, n. sp. Plate V., fig. 6. 



Sponge thin, encrusting. (The single specimen has evidently been removed from 

 the surface of some Alcyoriarian, the large calcareous spicules of which still adhere in 

 great numbers to the base of the sponge.) Surface uneven, corrugated, very slightly 

 hispid. Colour (in spirit) light brown ; texture rather friable. Vents and pores not 

 seen. Average thickness of specimen about 0'5 millim. 



The main skeleton consists of loose fascicles of tylostyles, springing from the base 

 of attachment and running to the surface, where they spread out in loose brushes and 

 give rise to the more or less hispid character. 



Spicules. (1.) Tylostyli (Plate V., fig. 6, a) ; straight, or nearly so, with large, oval 

 or sub-globular heads and rather slender, sub-fusiform shafts, gradually and usually 

 finely pointed at the apex. Size, when fully developed, about 0'38 millim. by O'OOG 

 millim. Many much more slender forms, with proportionally larger heads, sometimes 

 pear-shaped, also occur ; these I take to be immature spicules. 



(2.) Asters (Plate V., fig. 6, b, c, d); with strongly-curved centrum and stout, 

 conical, sharp-pointed, smooth spines (rays). The spines show a tendency in some cases 

 to arrange themselves in three groups, one group at each end of the centrum and one 

 in the middle, on the convex side of the curve. The middle of the concave side of the 

 centrum is free from spines, but the curvature is so great that this part of the 

 centrum is often concealed from view, and the spicule then resembles a spheraster. 

 The total diameter of the aster, when fully developed, is about 0'032 millim., but 

 numerous smaller (young) forms also occur. The asters are most abundant in the 

 dermal layer, where they form an almost continuous crust. 



This species finds a near relative in TOPSENT'S Hymedesmia, tristellata (14), from 

 Banyuls and the Azores. Closely similar asters occur in that species, but their rays 

 are often covered with minute spines, which I have never seen in the Ceylonese form. 

 I cannot agree with TOPSENT'S view that the " triple spherasters " (as he terms them) 

 have resulted from the concrescence of three centra covered with actines ; it appears 

 to me, on the other hand, that they have arisen by elongation of the centrum and 



R 



