16 Mr. H. J. Carter on a Siliceous Sand-Sponge. 



to which it is attached by a loose flocculent bundle of filaments 

 partially twisted into a spiral arrangement, either from the 

 eflfect of cmTents or the instinct of the organism, or both. 

 More detail I cannot offer, as I have given away the specimen. 



There is a bright yellow sponge of the same kind, but 

 growing in groups on the sandy bottom of the Mahim estuary, 

 off the Island of Bombay. Of this I possess no record what- 

 ever ; and the specimens were given away with that of Tethya 

 dactyloidea. 



I found many specimens of Tethya on the south-east coast 

 of Arabia, opposite to Ras Abu Ashrin, close to the north-east 

 end of the Island of Masira, where the land presents an ex- 

 panse, unbounded to the view, of white, dome-shaped, calca- 

 reous sand-hills, upwards of 100 feet high, forming the southern 

 part of the great Desert of Akhaf, with a very shallow shore 

 and soft sandy bottom extending for many miles out to sea. 

 Some of the specimens were alive, others dead, some floating 

 and free, others fixed to the few black basaltic rocks which 

 here and there skirt this otherwise all-white and desolate coast, 

 but most among the exuviae in the little bay at this point, 

 where, upon the stoneless and barren strand, lay heaped toge- 

 ther a mass of drift, looking more like an accumulation of 

 great bushes than zoophytes, which on my arrival they proved 

 to be. 



Here I saw more Tetliyadm than on any other part of the 

 coast. Those which were growing on the rocks adhered with 

 such pertinacity, and were so rigid and unyielding in structure, 

 that I could only get them off piece by piece with a hammer 

 and chisel. Like Actiniae, molestation appeared to increase 

 their rigidity. 



It might be assumed that the soft sandy nature of the shore 

 and sea-bottom on this part of the coast of Arabia is peculiarly 

 well adapted for the habitat of sponges generally and zoophytes, 

 of which the enormous amount of drift on the strand bore 

 ample testimony. 



The specimens of Tethya.^ as already stated, are found globu- 

 lar and floating, or hemispherical and fixed to the rocks, or 

 shaped like the one above described, throwing out a number of 

 radical fibres coral-like into the sand beneath, thus diftering 

 from those Spongiadas which seek a purer situation on the 

 sloping or undersides of rocks, where foreign particles fall off 

 rather than upon them. 



Calcareous Sponges. 



The spicules of Grantia ciliata among the Calcareous 

 Sponges, as well as those of Oorgonia and those of OpercuUna 



