19K CEYLON PEARL OYSTER REPORT. 



are attached to the substratum. All the tubes grow vertically upwards, close 

 together and parallel with one another, and they do not vary greatly in length. 

 Each terminates in a wide vent, which may be more or less closed by a membranous 

 sphincter. Colour in spirit, dull yellowish-grey. Texture of tubes compressible, 

 resilient, stiff; stem hard and tough. Total height of specimen 90 millims. ; length 

 of stem about 18 millims. ; diameter of stem about 10 millims. ; length of longest 

 unbranched tube about 52 millims. ; diameter of tube about 8 millims. The thickness 

 of the wall of the tube is about 2 millims., and the inner surface of the wall bears the 

 numerous small apertures of the exhalant canals, while the outer surface is granular 

 and porous in appearance and minutely hispid. 



The skeleton consists chiefly of very stout bands of spicular fibre, which run longi- 

 tudinally through the inner half of the tube-wall, branching and anastomosing with 

 one another in a quite irregular manner. From these stout fibres very short, irregular, 

 loose, somewhat plumose columns of long, slender spicules run almost vertically 

 outwards to the surface of the sponge, beyond which the apices of some of them 

 project ; the distance between the longitudinal fibres and the outer surface being 

 only about one spicule's length. No spongin is recognisable in ordinary unstained 

 sections. 



Spicules. Very variable in form and thickness, the stoutest being found for the 

 most part in the coarse longitudinal fibres, while more slender ones radiate thence to 

 the surface. The following may be regarded as the chief varieties : 



(1.) Styli (Plate XIII. , fig. 7, a, 6) ; fairly stout or slender, slightly curved, evenly 

 rounded off at the base, bluntly or sharply pointed at the apex ; size about 0'83 millim. 

 by 0'022 millim. ; passing into 



(2.) Oxea (Plate XIII., fig. 7, c), of about the same dimensions, but more or less 

 sharply pointed at each end. 



(3.) Strongyla (Plate XIII. , fig. 7, d, e) ; more or less crooked, often very much so ; 

 size, say, about 1'2 millims. by 0'022 millim. 



More slender forms of all occur, and the slenderer styli may be nearly as long as 

 the strongyla or much shorter than the stout styli whose measurement is above given. 



This species is evidently nearly related to Auletta lyrata, differing chiefly in the 

 arrangement of the skeleton and the length of the tubes. 



R.N. 73 (outside pearl banks, Gulf of Manaar) ; 148, 283 (fragment, both from 

 deep water oft Galle and onwards up West Coast of Ceylon). 



Leucophlceus, CARTER.* 



Axinellidse of massive habit, often clathrous. Skeleton reticulate, composed of stout 

 multispicular fibres with little if any spongin ; with a well-developed dermal 

 skeleton composed of a reticulation of spicule-bundles or a crust of tangentially 

 placed spicules. Megascleres typically stylote, sometimes oxeote. No microscleres. 



* rule CARTER (54), p. 323. 



