1921.] Fauna of the Chilka Lake .• Polychaeta. 573 



Diagrammatic Representation of the Parapodia. 



An effort has been made, by means of diagrammatic text-figures, to give a more 

 precise idea of the structure of the parapodium, and the distribution of the various 

 types of setae, than is possible in the usual method of illustration. In the latter, 

 the foot — the horizontal axis of which is at right angle to the main axis of the trunk 

 — is shown either from the anterior or posterior point of view. The text-figures now 

 endeavour to represent the foot diagrammatically as seen from the side, that is to 

 say, when looking at the distal end of the various lobes. The observer is supposed 

 to be looking at the parapodium on the right side of the specimen, so that the ante- 

 rior face of the parapodium is on the right, facing the head, and the posterior face on 

 the left, facing the tail. Further details are given on p. 576 and text-fig. 1. 



Material not pit por identification. 



For various reasons a small number of specimens in the collection were not iden- 

 tified. They were either too immature, or too imperfect, or (in one case) the preserv- 

 ing fluid had evaporated and the specimens had shrivelled up. They furnished 

 sufficient evidence, however, to prove the presence in fresh or brackish water, of a 

 number of additional species not described in the present report. Of special interest 

 was a tube of dried specimens from a canal of slightly brackish water at Durgapur, 

 near Calcutta, containing species of the genera Perinereis, Lepidonotus and Phyllodoce, 

 the two latter belonging to families not otherwise represented, whilst the Perinereis 

 sp. was distinct from P. marjorii of the Chilka Lake. 



Family HESIONIDAE. 



Ancistrosyllis constricta, sp. nov. 



(Plate XIX, figs. IA-IG.) 



This species, of which many individuals were taken, was found only in the Chilka 

 Lake. 



The general appearance of the body is very characteristic. The greatest width 

 is at the anterior end, the peristomial segment being the widest. The body narrows 

 rapidly as far as the 4th setigerous segment, this anterior region enclosing the large 

 thick-walled pharynx, which causes it to be circular in section. The body then 

 becomes flat, and on account of the greater size and length of the parapodia, it seems 

 to increase considerably in width, but in reality the trunk, after a slight increase, 

 remains the same width for some distance, and then gradually tapers towards the 

 tail. The body has thus a distinct neck, or waist, and hence the specific name. 

 Towards the posterior end the ventral surface becomes rather more convex, and the 

 feet appear to be on the dorso-lateral surface. 



The peristomium and three anterior setigerous segments (fig. ia) are longer 

 than the succeeding ones, and are only separated from each other externally by very 

 indistinct grooves. 



In the largest individuals the posterior region is absent. A fragment, 23 mm. 



