86 EECORDS OF THE AITSTRALIAN MUSEUM. 



digitata — have been examined. Thalassodendron typica and T. 

 viminalis are quite distinct. T. brevispina, T. paucispina, T. 

 ruhens and its varieties dura and lamellosa, are very similar in 

 external appearance, especially as to surface, differing slightly 

 in habit but very little in their spicular characters. From a 

 large well grown specimen it would be possible to select portions 

 which might be passed as distinct species or varieties if the habit 

 and general appearances alone were considered, the rest of the 

 characters do not differ very materially. It is indeed highly 

 probable that the above forms represent one variable species. 

 They are all characterised by having a white incrustation, — when 

 perfect consisting of a porous layer of stylote spicules. When the 

 dermal layer is removed, the surface is hispid ; a character which 

 is well illustrated in Clathria lendenfeldii, Ridley and Dendy.^^ 



The following descriptions are based on the examination of the 

 types :— 



Thalassodetidron typica, Lendenfeld, (No. 364). 



This specimen consists of a shallow vase-shaped sponge, which 

 has been bisected. In appearance it resembles a washed-out 

 Chondropsis, but the lamina is much thinner than in any species 

 in that genus. The published description agrees with the speci- 

 men as far as the habit is concerned. The fibres and spicular 

 characters do not agree with the diagnosis. The main fibres are 

 densely charged with smooth oxeote spicules, held together by 

 very little obvious spongin. Smooth "straight styli" are extremely 

 rare. The connecting fibres are stated to be "aspiculous." I 

 failed to find any such aspiculous fibres ; even the finest consist of 

 an axial thread of spicules, with just a trace of investing spongin. 

 Both kinds of fibres are echinated by spined styli ; and smooth 

 styli, if present as echinating spicules, are accidental and belong 

 to the axial thread, they are not echinating in the strict sense of 

 the term. 



Megascleres — (a) Spined echinating styli, rather blunt at the 

 apex. Size^O'l by O'OOl mm. (b) Slightly curved smooth oxea, 

 abruptly but rarely acutely pointed. Size — 0*02 to 0'035 by 

 0065 to 0-012 mm. (c) Straight smooth styli. Size 0-8 to 1 

 by 0-0015 mm. 



Thalassodendron rubens, Lendenfeld, (No. 286). 



The type is a washed-out specimen, having been purposely 

 reduced to a skeleton when obtained. The spicules are as follows: 



Megascleres — (a) Spined styli, rather scarce. Size — 0-06 by 

 0-007 mm. {b) Stout smooth styli. Size— 0-15 by 001 mm. 

 (c) Medium smooth styli. Size — 0-17 by 0-005 mm. [d) Slender 

 smooth styli. Size 0-12 by 0-0015 mm. 



18 Bidley and Dendy — Chall. Rep., Zool., xx., 1887, pi. xxviii., %. 5. 



