568 M emoirs of the Indian Museum. [Vol. V, 



in the Chilka Lake and the Cochin Backwater. So few species were found in the 

 latter locality that it may be left out of further consideration. As regards the Chilka 

 Lake and the Gangetic Delta, in the almost complete absence of any knowledge of 

 the species comprising the Polychaete fauna of the Indian littoral, it is quite impos- 

 sible to reach any reliable conclusions as to whether the species here described are 

 peculiar to, or specially adapted to survive in the euryhaline conditions in which they 

 occur. Nevertheless, certain opinions which I have formed may be stated for what 

 they are worth. The collection of species from the Chilka Lake has a typically 

 marine facies. It probably represents an impoverished remnant of the Polychaete 

 fauna which inhabited the open bay before the present lake was almost completely 

 cut off from the sea by the spit of sand which forms its eastern boundary (vide 

 Annandale and Kemp, 1915, p. 5). How far the species living in the Chilka Lake have 

 been differentiated from their relations still probably living in the adjacent open 

 sea, in order to fit themselves for the altered environment, cannot at present be 

 stated, but the changes have probably not been great. It seems likely that only 

 those species survived which already had the capacity to withstand great variations 

 of salinity. This point receives further consideration below (p. 571). 



The group of species found in the Gangetic Delta conveys the impression, in a 

 rather vague manner, of having undergone greater modification than the Chilka Lake 

 group. The eight species found here are all new to science, and two of them belong 

 to genera previously undescribed. All the species possess branchiae, or analogous 

 organs for performing the function of respiration. Six of the species belong to genera 

 which have seldom or never been found before. Speculations of this nature, however, 

 will have greater claims to validity when the whole fauna of the two areas is taken 

 into consideration. In other groups of animals, the species common to the Chilka 

 Lake and the Gangetic Delta are more numerous (Annandale and Kemp, 1915, p. 15). 



Distribution of Poeychaeta in the Chieka Lake. 



For a full account of the conditions, topographical and hydrographical, prevail- 

 ing in the Chilka Lake, reference must be made to the account given by Annandale 

 and Kemp (1915, p. 1). For our purposes, a very brief description will suffice. The 

 Chilka Lake is on the east coast of India, and is connected by a very narrow opening 

 with the Bay of Bengal. It lies mostly in Orissa, but the southern extremity extends 

 into the Madras Presidency. It is about 40 miles long, the greatest breadth is 12^ 

 miles, and it occupies an area of about 350 square miles. It is divisible into two well- 

 defined areas, where the biological and physical conditions are very different. There 

 is the main area, a shallow lagoon 4-8 feet deep in the dry season, 10-15 feet in the 

 wet season. The northern part of the lake is very shallow, and very few Polychaeta 

 were collected there. The bottom of the lake is predominantly muddy, though on the 

 shores of some of the islands, and at the south-western extremity there is an admix- 

 ture of sand. Near the middle of the eastern shore there is a shallow bar leading 

 into a narrow channel about 12 miles long and a mile wide, which connects the lagoon 

 with the Bay of Bengal, the outer opening being only several hundred yards wide. The 



