52 Memoirs of the Indian Museum. [Vol. V, 



in its mechanism and functions^ to that of Polyzoa Phylactolaemata and have 

 suggested that in both cases the bladder-like body is an adaptation for life in fresh 

 water. The fresher water is, the lower its specific gravity. The yolk contained in 

 larvae that grow without feeding is heavy, and a body that has to progress through 

 fresh water to obtain a situation suitable for subsequent changes is greatly hindered 

 if it is much heavier than the medium through which it moves. If it is hollow, and 

 if the cavity is filled with water, as that of the larvae under consideration presum- 

 ably is, the weight of the yolk is compensated for and the specific gravity of the 

 moving body becomes practically identical with that of the surrounding medium. 

 The cavity in the larva of L. lacustris is not relatively so large as that in the larvae 

 of Spongilla, Nudospongilla and Ephydatia, nor has it the same specialized structure, 

 but it is at any rate considerably more ample than in most marine types. Its size 

 is, therefore, not improbably correlated with the fact that the larva lives in water 

 of low salinity and consequently of low specific gravity. 



L. lacustris is too thin a sponge to afford shelter to any but very small animals. 

 Nematode worms (Dorylaimus sp.') are, however, common in its canals;' at least 

 one minute species of tubicolous polychaete, probably a Capitellid, was found on 

 one occasion, while another, tubicolous and plumigerous species is nearly always 

 abundant. The rhizomes of the Hydrozoon Bimeria fluminalis and the Polyzoon 

 Loxosomatoides laevis are also often found at the base of the sponge, sending up their 

 branches or polyps through its substance to the surface. Lamellibranch molluscs of 

 the genus Modiola are sometimes overwhelmed in its growth. 



Grade TETRACTINELLIDA. 



Suborder SIGMATOPHORA. 



Family TETILLIDAE. 

 Genus TETILLA, Schmidt. 

 [Tetilla dactyloidea (Carter) .-J 

 1869. Tethya dactyloidea, Carter, .47m. Mag. Nat. Hist. (4) III, p. 15, fig. 



id. , (4) IX, p. 82, pi. x, figs. 1-5. 

 ,, id. , Journ. Linn. Soc. Zool. (Fauna Mergui, I), p. 79. 



,, Sollas, ' Challenger ' Rep., Zool. XXV, p. 1. 



,, Keller, Zeitschr. wiss. Zool. LII, p. 335. 

 ,, v. Lendenfeld, Das Tierrech, Tetraxonia, p. 18. 



Distribution: S.Arabia; Bombay; Mergui Archipelago, Burma {Carter). 



The typical form of T. dactyloidea was not obtained in the Chilka Lake, but 

 another, so near that I think it must be regarded as a variety, is represented in 

 our collection by several specimens. For this form I propose the name lingua in 

 reference to its peculiar shape. 



J Stewart, Rec. Ind. Mus. X, p. 247. When Capt. Stewart's paper was written L. lacustris was 

 not distinguished from L. aquae-dulcioris. 



1872. 



y y 



1887. 



> > 



1888. 



Tetilla 



1891. 



y > 



1903. 



j > 



