POLYCHAETA. 



By Rowland Southern. 



INTRODUCTION. 



It was considered advisable, whilst describing the Polychaeta from the Chilka 

 Lake, to examine also those species of the group in the Indian Museum which, at 

 various localities in India, had been found in water which was either fresh or periodi- 

 cally mixed with fresh water, or in other words was not distinctively marine. The 

 collection contains very few species which spend their whole lives in fresh water. 

 The majority live either in brackish water of low salinity, or belong to the "Eury- 

 haline " group. The latter term was first used by Moebius to designate those species 

 which can live in water the salinity of which varies between wide limits. In Europe 

 very few species of Polychaeta can tolerate marked changes in the salinity of the sea- 

 water and fewer still can reproduce under such conditions, but in India, judging from 

 the list of species dealt with in the present paper which is obviously far from ex- 

 haustive, they are relatively far more numerous. This adaptation may be correlated 

 with the sharp division of the climate into wet and dry seasons, whereby the littoral 

 region is periodically flooded with water of low salinity, especially in bays and 

 estuaries. 



From the whole of India only two species of Polychaeta have been recorded 

 from fresh or brackish water. These are Matla bengalensis Stephenson (1908, 

 p. 39 and 1910, p. 82) and Spio bengalensis Willey (1908, p. 389) both from brackish 

 pools at Port Canning, L,ower Bengal. Matla bengalensis is based on juvenile speci- 

 mens of a Capitellid, and neither it nor Spio bengalensis were represented in the 

 present collection. Records of littoral marine Polychaeta from Indian shores are 

 practically absent. A number of species have been recorded from Ceylon by 

 Schmarda, Grube, Michaelsen, and Willey. It is therefore not surprising that almost 

 all the species in the present paper are new to science, especially when one remem- 

 bers the peculiar nature of the habitat in which they have been found. Many of the 

 species of Polychaeta known from the Indian Ocean and South Pacific have been very 

 imperfectly described and inadequately figured, judged by modern standards. Any 

 specimens now referred to such species would be involved in a cloud of uncertainty, 

 and it seems preferable, where there is any doubt, to ignore them until they have 

 been redescribed from trustworthy material. 



List of Speciks. 



Ancistrosyllis constricta, sp. nov. Chilka Eake. 



Lycastis indien, sp. nov. Gangetic Delta ; Cochin Backwater. 



