i)8 (T.YLON PEARL OYSTER REPORT. 



others a little shorter, and the fourth much shorter; (/>.) with one very short 

 unbranched ray (shaft) and three much longer rays (cladi), of which two are forked ; 

 cladi of somewhat unequal length ; maximum diameter of cladome from tip to tip of 

 rays 0'276 millim. ; maximum diameter of cladi about O'OIGG millim. ; (c.) similar to 

 (a.), but with cladi much curved ; the very short shaft, as is commonly the case, 

 rounded off at the extremity; (d.) with only three rays, two almost in the same 

 straight line and the third, much shorter (? = shaft) at right angles to them ; length 

 of each of longer rays about 0'147 millim. ; of short ray about 0'055 millim. The 

 rays of these spicules are often irregularly bent or curved. They are probably, ;is 

 pointed out by CARTER and SOLLAS in the case of P. merguiensis, modified " zone- 

 spicules " (plagiotrisenes). 



(2.) Protrifenes (Plate III., fig. 7, e, e'}; few in number and very variable in 

 dimensions, with shaft and cladi all very slender or fairly stout, and cladome some- 

 times irregular. The cladome may or may not project beyond the surface. 



(3.) Anatrifenes (Plate ILL, fig. 7, f, f); with short, stout cladi, and very long 

 slender shaft, often inflated in a bulbous manner at a short distance below the 

 cladome and tapering to hair-like dimensions at the other end. Length of shaft in 

 measured specimen 3 '3 millims. ; diameter between bulb and cladome 0'007 millim. ; 

 length of cladi 0'027 millim. The cladomes of these spicules sometimes project 

 beyond the surface of the sponge. 



(4.) Oxea of the main skeleton (Plate III., fig. 7, g, g', g'') ; stout, straight or 

 nearly so ; fusiform, with the ends gradually and finely pointed, or more or less 

 irregular ; size about 2'9 millims. by 0'0365 millim., but usually more slender. 

 Numerous much smaller oxea, apparently young forms, also occur. 



(5.) Sigmata (Plate III., fig. 7, k) ; extremely slender, frequently, if not always, 

 contort, about 0'014 millim. from bend to bend ; abundant. 



In stained sections of the largest specimen the cortex measures up to about 

 0'28 millim. in thickness. It is composed of a compact tissue which appears to be 

 cy stench ymatous rather than collenchymatous, and the cells contain numerous minute 

 brown pigment granules. The choanosome appears to be mostly collenchymatous and 

 contains brown pigment granules similar to those of the cortex, but fewer in number. 

 The flagellate chambers are oval or nearly spherical, up to about 0'0249 millim. in 

 diameter. 



This interesting sponge is evidently nearly related to CARTER'S Tethya merguierusi* 

 (21) (Tetilla merguiensis of SOLLAS) from the Mergui Archipelago, off the coast of 

 Burmah, but differs to such an extent that there can hardly be any question of 

 specific identity. The characteristic inhalant pore-sieves and dermal reticulation of 

 CAHTKR'S species are not recognisable here ; the dermal microxea are absent, and the 

 modified " zone-spicules " appear to be much more irregular in shape. 



R.N., 184, 187 (Stat. VI., Muttuvaratu Paar, Gulf of Manaar) ; 214 (deep water 

 outside pearl banks, Gulf of Manaar) ; 245 (Ceylon seas). 



