50 Records of the Indian Museum. [Vol.. VI, 



regular snail-shell fashion in their oldest portion, and although they 

 become uncoiled and very irregularly spiral in their distal parts, 

 adopt a course much nearer the vertical than that adopted by Sp. 

 cummingi. The shell is thicker and stouter than that of the 

 Spiroglyphus. The difference in growth between the two shells 

 appears to produce or at any rate to be correlated with structural 

 differences in the sponge associated with them, for there can be no 

 doubt that the same species of sponge is associated with both 

 molluscs. 



Unfortunatel}^ our data as regards the provenance of the two 

 species of shell with their associated varieties of sponge are not 

 sufficiently^ precise for it to be possible to say whether they affected 

 habitats in any way diverse. All that we know is that both 

 species are common in an area that extends in a southerly direc- 

 tion from opposite Gopalpur on the coast of the Ganjam district 

 at least to the neighbourhood of Vizagapatam, and that they are 

 found in depths of between 15 and 30 fathoms. 



The sponge Racodiscula sceptrellifera belongs to the Tetracti- 

 nellid grade Lithistida, which is characterized b}^ the possession of 

 much proliferated spicules (primarily of the Tetractinellid type) 

 welded together to form a compact siliceous skeleton. This skele- 

 ton, even after the death of the sponge, can be broken up only b^^ 

 the exercise of considerable violence. 



It is probable that the masses, with which this paper deals, will 

 be of considerable interest to the geologists of some future epoch, 

 when the bottom of the Bay of Bengal has become dry land, if 

 there be geologists then. This is especially the case as regards 

 those masses in the formation of which Racodiscula plays a part, 

 for,'' Thelyithistids are peculiarly wellsuitedfor preservation, owing 

 to the massive, stony character of their skeletons ; and their re- 

 mains occasionally form thick deposits, especially in the Jurassic 

 and Cretaceous." (Zittel's Text-Book of Palaeo7itology, vol. i, 

 p. 47, Engl, ed., 1900.) We have no evidence, however, that the 

 combined growth of the shells and the sponges is producing in 

 Indian seas, reefs at all comparable to those now being formed b}- 

 Vermetid shells alone off the coast of Florida. These reefs are 

 described by Dall ^ as being of sufficient size for boats to be 

 wrecked upon them at low tide, and as covering very large 

 areas. But it is evident that masses of considerable weight and 

 stability, a d possibly larger than any that have as yet been ex- 

 amined, are being produced in enormous numbers off" the coast of 

 the Ganjam and Vizagapatam districts of the Madras Presidency. 

 From a practical point of view these masses would interfere seri- 

 ously with trawling operations off this coast, for the net of the 

 " Golden Crown " was seriously damaged by them on more than 

 one occasion ; from a zoological point of view they seem to be 

 characteristic of a definite faunistic area of somewhat limited 



• Bull. Mus. Zool. Harvard, xviii, p. 262 (1889). 



