80 CEYLON PEARL OYSTER REPORT. 



dense brushes of trisenes whose cladomes lie at varying depths beneath the dermal 

 membrane, but never very deeply. The dermal membrane is strengthened by a thin 

 crust of spinose microstrongyles, interrupted by the very numerous dermal pores. 

 The minutely hispid character of the surface is due to the presence of very slender, 

 hair-like anatrisenes projecting beyond the dermal membrane. 



Spicules. (1.) Plagiotriaenes (almost orthotrisenes) (Plate III., fig. 1, a, b) ; with 

 long shaft tapering very gradually to a sometimes almost filiform extremity, and 

 rather short, stout, sharply pointed or rather blunt cladi ; shaft about 1 '5 millims. by 

 0'033 millim., with cladi about 0'148 millim. by 0'027 millini. 



(2.) Plagiotrisenes (almost protrifenes) (Plate III., fig. 1, c, c') ; with long, slender 

 shaft tapering to almost hair-like dimensions, and short conical cladi projecting 

 forwards at an angle of about 45; shaft about 1'8 millims. by 0'0094 millim. ; cladi 

 about 0'028 millim. by O'OOS millim. Not very numerous. 



(3.) Anatriaenes (Plate III., fig. 1, d, d') ; with long, slender shaft and short, sharp- 

 pointed, strongly recurved cladi ; cladome somewhat flattened in front ; shaft and 

 cladi of about the same dimensions as in the preceding. 



(4.) Very slender, hair-like anatriaenes with minute cladomes projecting beyond the 

 surface of the sponge. These spicules seem to be fairly numerous and characteristic, 

 but the cladomes are nearly always broken oft' in the preparations. 



(5.) Oxea (Plate III., fig. 1, e) ; long and comparatively slender, usually slightly 

 curved ; fusiform ; gradually and usually sharply pointed at each end ; measuring, 

 when fully developed, about 1'8 millims. by '037 millim. 



(6.) Chiasters (Plate III., fig. 1,0); with little or no centrum and very slender, 

 cylindrical, very minutely roughened, tylote rays ; total diameter up to about 

 0-016 millim. 



(7.) Microstrongyla (Plate III., fig. I,/) ; straight, rather slender and minutely 

 spined or roughened ; measuring up to about 0'02 millim. by 0'002 millim., most 

 abundant in the dermal membrane, but also plentiful in the choanosome. 



There is a well-developed cortex about - 25 millim. thick, composed of a mixture 

 of chondrenchymatous, collenchymatous, and fibrous tissue, the first-named developed 

 chiefly towards the outside and the last towards the inside. The mesogloea of the 

 choanosome is finely granular, but with an admixture of colleuchymatous and 

 choudrenchymatous tissue. The flagellate chambers are approximately spherical, 

 about 0'02 millim. in diameter, and eurypylous. The dermal pore-sieves form the 

 thin roofs of wide chones, which pass vertically through the cortex and are continued 

 directly into the inhalant canals of the choanosome, without any specially differentiated 

 subcortical crypts. 



The presence of a fibrous cortex, though not very strongly developed, seems to 

 indicate SOLLAS'S genus Psammastra for this species, which is nearly related to three 

 sponges described by Mr. CARTER under the names Stdletta gevdides (18),* Stelletta 

 * Vide also SOLLAS, " Challenger " Tetractinellida, p. 200. 



