I ID CEYLON PEARL OYSTER REPORT. 



are abundant between the stout horny fibres, as well as (sometimes) in their axes. 

 The species has also been recorded from off Bahia (" Challenger "). 

 R.N. 8, <J, 38 (all three from Gulf of Manaar) ; 351 (Ceylon seas). 



Toxochalina robusta, var. ridleyi, nov. Plate IX., fig. 2. 



The type specimen is very irregular in shape ; massive and angular, with a slight 

 tendency towards branching. It has evidently been attached by a broad base to one 

 valve of a Lamellibranch shell (1 Margaritifera vulgaris), the impress of which is still 

 clearly visible. The surface is smooth and sub-glabrous, but uneven and very 

 distinctly granular when viewed under a lens. The vents are rather numerous (live), 

 about 4 millims. in diameter, with very prominent margins ; each is the opening of a 

 wide, deep oscular tube of the same diameter as itself. The texture (in spirit) is com- 

 pressible and resilient, but stiff and tough. Colour, pale brown. The specimen is 

 about G6 millims. long, 38 millims. broad, and 31 millims. high. 



The main skeleton is a reticulation of horny fibre, with very few and slender 

 spicules (Plate IX., fig. 2). The primary fibres are very stout, sometimes as much as 

 0"164 millim. in diameter, but very variable ; typically they run at right angles to 

 the- surface and are united by short secondaries to form rectangular meshes, but the 

 network often becomes very irregular and the size of the meshes is very variable. 

 The secondary fibres are usually, but not always, more slender than the primaries. 

 The primaries are cored by a multispicular axis of slender oxea arranged in a plumose 

 manner (as in typical Axinellidas), but all entirely enveloped in spongin to such an 

 extent that the entire column of spicules only occupies one-third (or less) of the 

 thickness of the fibre. The secondary fibres contain only a few isolated spicules 

 arranged uniserially. 



The dermal skeleton consists of a rather close-meshed reticulation of rather slender, 

 unispicular horny fibre. From the nodes of this reticulation brushes of oxeote spicules 

 project vertically. In certain places this dermal skeleton appears to become many 

 layers deep, and the vertical brushes of oxea are continued inwards as more or less 

 plumose columns enveloped in spongin and connected by numerous unispicular cross- 

 fibres, so as to form a close skeleton network beneath the surface, very consjucuous 

 in vertical section, and strongly contrasted with the much coarser, more widely 

 meshed and less abundantly spicular main skeleton below it. 



Spicules. (1.) Oxea (Plate IX., fig. 2, o) ; short and rather slender, slightly curved, 

 fairly gradually sharp-pointed at each end ; measuring about 0'08 millim. by 0"004 

 millim. near the surface, but usually smaller, and especially more slender, in the fibres 

 of the main skeleton. These spicules at any rate, in the main skeleton are 

 evidently becoming vestigial. 



(2.) Toxa (Plate IX., fig. 2. t) ; slender, more or less strongly curved in the middle, 

 very slightly re-curved at the apices ; sometimes slightly roughened in the middle, 

 gradually sharp pointed at the ends; size varying up to about - 08 millim. (in a 



