1921.] Fauna of the Chilka Lake : Polychaeta. 581 



hemigomphs shown in fig. 2G), the lower group consisting of a number of falcate 

 heterogomphs, the lower ones having shorter tips than the upper ones. Horst' s 

 description is substantially similar. Thus the present species differs from L. hawaii- 

 ensis in having falcate heterogomphs above the spine, and heterogomphs with long 

 coarsely serrated tips below the spine. Horst found in the dorsal lobe of the 41st 

 foot of one specimen " a faintly developed setose bristle." 



In the present state of our knowledge of the genus Lycastis, this form has as 

 much claim to specific rank as any of the previously described species. Sufficient 

 attention has not been given to the precise arrangement and structure of the setae. 

 On the other hand, too much significance has been attached to slight differences in 

 the arrangement of the eyes. 



The following six species of Lycastis, characterised by the great enlargement of 

 the posterior dorsal cirri, have been described : — 



L. brevicornis, Audouin and Milne-Edwards. Noirmoutiers (France). Marine. 



L. abiuma, Grube. Desterro, Brazil. Marine. 



L. senegalensis, de Saint-Joseph. Marsassoun (100 kilometres from the sea) 

 Senegal, West Africa. Brackish water. 



L. ouanaryensis, Gravier. French Guiana. Marine and freshwater. 



L. Geayi, Gravier. French Guiana. Freshwater. 



L. hawaiiensis, Johnson. Hawaii and Java. Freshwater. 



L. Geayi is sufficiently characterised by the complete absence of falcate setae. 

 In L. brevicornis, L. abiuma, L. senegalensis, and L. hawaiiensis, the heterogomph 

 setae with coarsely serrated tips have not been described. There remains L. ouanar- 

 yensis, which was found both in the sea and in freshwater in French Guiana, on the 

 north-east coast of South America. The similarities between this species and L. indica 

 are very striking. The setae are very similar in arrangement, and the ventral division 

 of the middle and posterior feet contains heterogomph setae with slender coarsely 

 serrated tips, exactly as in L. indica. The anterior part of the body is rose coloured, 

 the posterior green. The very slight distinctions between the two forms are as 

 follows : — In Gravier' s species (1) the longitudinal median groove on the head runs 

 back to the buccal segment ; (2) the eyes are devoid of lenses ; (3) the tentacular 

 cirri are shorter than in L. indica ; (4) the jaws have six teeth, as against nine in L. 

 indica ; (5) the dorsal cirri of the posterior segments are longer than in L. indica ; 

 (6) the dorsal division of the foot contains 2 or 3 setae, and the falcate setae have 

 tips of rather different shape. 



L. indica is intermediate between L. hawaiiensis and L. ouanaryensis as regards 

 the setae. It agrees with the former in the great reduction of the dorsal division of 

 the foot, and with the latter in the presence of the coarsely serrated heterogomph 

 setae. 



Habitat. This species was obtained from the three following localities : — 



In rotting cocoa-nut shell floating in the Beliaghatta Canal, near Calcutta, 

 26. viii. '09. Water slightly brackish. In the same tube was a specimen of the 

 freshwater Oligochaete, Branchiura sowerbyi, Beddard. 



