1915.] Fauna of the Chilka Lake : Sponges. 49 



There is no orifice, but the coat, which is about 0*007 mm. thick, is deposited 

 in several layers, between which there is air or some other contained gas, so that, 

 when dry, the structure has a slight silvery lustre. The gemmules vary in size, but 

 the greatest transverse diameter does not exceed 0*21 mm. The biological signifi- 

 cance of the whole structure is discussed below (pp. 51, 52). 



The larvae (fig. iia) is, when set free, a minute ovoid body distinctly truncated 

 at the broader end. Its colour is a uniform clear yellow not quite so deep as that of 

 the gemmules. Cilia cover the whole external surface except the broad truncated 

 end, which forms a hernia of relatively large cells. I have not been able to make a 

 detailed examination of living material, but in well-preserved and stained specimens 

 the cells of the external ciliated epithelium (endoderm) seem to be slightly elongated 

 immediately round the hernia. There is, therefore, reason to think that a ring of 

 longer cilia surrounds this region. The greatest length (in Canada balsam) is about 

 0-139 mm. , and the greatest width about 0-102 mm. A distinct segmentation-cavity 

 of irregular shape and relatively large size can be detected in the interior of the 

 larva anterior to the mass of enlarged cells that forms the (posterior) hernia. 

 A single fascicle of spicules is already present. Although the spicules are very 

 slender, they are clearly tylostyles with a distinct head. Their heads rest, approxi- 

 mately in a ring, a little in front of the enlarged cells ; their shafts point forward 

 and a little outwards and lie to a considerable extent in the segmentation-cavity- 

 Their points are separated by a considerable distance from the anterior extremity. 

 The fascicle is composed of about 7 spicules. 

 Type. No. Z.E.V. 6442/7. Ind. Mus. 



L. lacustris has been found as yet only in the main area of the Chilka L,ake, in 

 which it occurs abundantly, often together with Spongilla alba, wherever there are 

 rocks or stones at the edge. It can live, at any rate for a season, in pure fresh 

 water and has not yet been found in that of a greater sp. gr. than 1-0150. It grows 

 at all times of the year, but is most vigorous at the season when the water of the 

 lake is brackish but the level still fairly high (that is to say about December and 

 January), and occurs in depths of from a few inches to at least 2 fathoms. 



It is with considerable hesitation that I describe this sponge as a species distinct 

 from L. aquae-dulcior is, but on the whole, to do so seems less liable to cause confusion, 

 should my opinion be ultimately proved incorrect, than to regard the sponge, without 

 experimental evidence, as merely a highly specialized phase of that species. The 

 most important differences between the two forms are the following : — 



1. The spicule-fibres of L. lacustris are longer, branch more freely and maintain 

 a horizontal direction for a greater part of their length than those of 

 L. aquae-dulcioris. 

 ■ 2. The spicules are even more variable in size but have spherical or slightly 

 elliptical heads in a great proportion of instances ; some of them are 

 always considerably larger than any of those of L. aquae-dulcioris. 

 3. The gemmules are piled together in L. lacustris, one on the top of another in 



