PLATE XCI. 337 



larger and more numerous than near the middle of the 

 cloaca. The oscula can rarely be seen on the outer 

 surface, the abundance of the long, slender, defensive 

 spicula entirely obscuring them ; those seen on the 

 inner surface were in an open condition. 



The skeleton structures in this species are remark- 

 ably delicate and slender. In the mass of the sponge 

 and in the cloaca3 the skeleton is composed of very 

 numerous, equi-angulated and rectangulated, triradiate 

 spicula, closely matted together, with an intermixture 

 of the long, slender, acerate ones. In the cloacal 

 organs the latter form are disposed without any 

 apparent order, but in the mass of the sponge they 

 frequently assume a subfasciculate mode of deposi- 

 tion. 



The normal forms of the skeleton spicula are purely 

 equi-angulated and rectangulated, triradiate, the 

 former predominating greatly in number ; but it is 

 a singular fact that neither form is frequently found 

 in a normal state, their radii in almost every one 

 being more or less distorted, indeed the distortion 

 appears to almost amount to the rule instead of the 

 exception. 



The distortion of the radii of triradiate skeleton 

 spicula is evidently caused by the closely felted mode 

 of their disposition. The extreme expansion of two 

 of them measured, was -3^7 and g-J-g inch. 



The spiculated triradiate internal defensive spicula 

 of the large description of cloacae were of the same 

 size as those of the skeleton ; the spicular ray being 

 straight and of about the same length as the other 

 three. They did not appear to be very numerous, and 

 the spicular ray is projected at about right angles, to 

 the inner surface of the cloaca. 



The only other known British calcareous sponge 

 with which this species is likely to be confounded is 

 Leucosolenia botryoides, and then only in its young and 

 immature state ; but even in this condition it is, by 

 careful microscopical examination, readily to be sepa- 



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