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



on the coast north of Palk Straits differ greatly from those occurring in the Gulf of 

 Manaar, whence several large collections have been described. It is not surprising, 

 therefore, that the Chilka sponges cast little light on the distribution of the Indian 

 sponge-fauna as a whole. Of the two Spongillidae one is apparently endemic in the 

 lake, while the other has been found in Egypt as well as in different parts of India. 

 The species belonging to marine families also are for the most part either endemic or 

 of wide distribution. To the latter category belong Cliona vastifica, which is cosmo- 

 politan, and Subevites sericeus, an Indo-Pacific species originally described from 

 Japan and not as yet found in any intermediate locality. Tetilla dactyloidea, of 

 which the variety lingua is apparently endemic, is known from the Arabian Sea and 

 from the Mergui Archipelago on the east side of the Bay of Bengal. Both species of 

 Laxosuberites , so far as their distribution is at present known, are confined to lagoons 

 on the east coast of India and it is not improbable that L. lacustris may have been 

 evolved from L. aquae-dulcioris in the Chilka Lake. 



The main interest of these sponges is, as I have already indicated, of a strictly 

 biological nature. Attention may be drawn in the first place to the remarkable varia- 

 tions exhibited by most of the species and to the fact that these can be definitely 

 correlated with differences in environment. It is evident that all the species in the 

 list are able to withstand, by one means or another, great changes of salinity. The 

 peculiar modification of the simple gemmule characteristic of the Suberitidae whereby 

 Laxosuberites lacustris has fitted itself to survive periodical desiccation (p. 50) is a note- 

 worthy instance of adaptation to environment —a series of phenomena also illustrated 

 to a degree hardly less striking by the manner in which the skeleton of Spongilla 

 alba is modified to withstand the violence of the waves in exposed positions in the 

 lake (p. 28). 



The only sponge not included in the Chilka fauna with which I am acquainted 

 from other Indian lagoons or estuaries is a minute representative of the order 

 Myxospongida found in October, 1913 on oyster-shells in the backwater at Ennur a 

 few miles north of Madras. It accompanied Laxosuberites aquae-dulcioris , to young 

 examples of which it bore so close a resemblance in the field that I failed to distin- 

 guish the two species. Specimens were therefore preserved without any special care 

 and are so shrivelled and distorted that I can only say in reference to them that they 

 seem to represent an undescribed genus. I failed to find this sponge again at En- 

 nur in January, 1915. 



The table on the opposite page shows at a glance the distribution, in the Chilka 

 Lake and elsewhere, of the different species. The names of those that are apparently 

 endemic are marked with a star. 



For particulars as to the biological conditions that prevail in different parts of 

 the Chilka Lake at different seasons reference may be made to the Introduction to 

 this volume. The specific gravities of water quoted in the paper are not readings 

 obtained in the field but have been corrected to a standard temperature of I5°C. 



