1921.] Fauna of the Chilka Lake : Polychaeta. 641 



merits are usually swollen, and the inter-segmental grooves are faint. Behind the 

 5th (the 4th setigerous) and the succeeding segments the grooves are deeper, and 

 there are faint transverse grooves in line with the setae. Beginning on the ist seti- 

 gerous segment there is on each side of the body a shallow groove, and these, com- 

 bined with the broad and shallow ventral groove, produce two ventro-lateral ridges, 

 carrying the ventral setae, somewhat in the manner of Atnmotrypane. The ridges 

 fade away in the middle of the body. 



The thorax consists of 12 segments, the ist being achaetous. The 5 anterior 

 setigerous segments have rather short capillary setae in both dorsal and ventral 

 bundles. The dorsal setae (fig. 23F) have broad tapering wings. The ventral setae 

 are very similar, except that the wings are rather narrower, more elongate, and 

 proximally do not taper so gradually. There are 7-15 setae in the dorsal bundles, 

 4-14 in the ventral bundles. In the ist and 2nd feet the dorsal setae are in two 

 rows, in the other bundles only in a single row. In the 7th-i2th segments all the 

 bundles are composed of long crochets (fig. 23G). The distal quarter is widened, and 

 enclosed in a sheath. The shaft narrows beneath the tip, which has a large tooth, 

 with two small and indistinct spines on the crest. The shaft is long, doubly curved, 

 and has no nodular swelling. 



In the ist setigerous segment the dorsal bundles of setae are separated by a space 

 rather greater than that which separates the dorsal and ventral setae on each side. 

 In the subsequent thoracic segments this interval is only slightly reduced, but in the 

 12th setigerous segment — the ist abdominal — the dorsal bundles lie close together near 

 the median line. The setae in the abdominal segments are surrounded by tumid 

 lips, which are absent in the thoracic segments. 



In the thoracic segments the setae lie in the middle of the segment, but in the 

 abdominal region the setae are near the posterior border. Furthermore, in the 

 anterior region the segments are as long as broad, but they gradually shorten, till in 

 the mid-region they are three or four times as wide as long. The length again 

 increases in the posterior region till it equals half the width. In the middle of the 

 body the constrictions between the segments are very deep, especially in the dorsal 

 region. The abdominal setae are all very short crochets (fig. 23H), and have a nodu- 

 lar swelling in the middle of the shaft. There are 10-15 of them in each bundle. 



The structures which, in this genus, are supposed to have a branchial function, 

 consist of a number of lobes projecting from the posterior part of each segment. 

 There are two of them on the dorsal surface (fig. 23c), carrying the dorsal setae, two 

 in the latero-ventral region (figs. 23D, 23E) carrying the ventral setae, and one in the 

 mid- ventral region, overlying the nerve-cord. The dorsal lobes, which make their 

 appearance near the 100th segment, are by far the most conspicuous. The ventral 

 lobes appear near the 140th segment, and are smaller and more rounded than the 

 dorsal pair. In the last few feet the branchial lobes are small and inconspicuous/ 

 In other specimens the branchiae are on fewer segments, but this may be due to re- 

 generation of the posterior region. 



The anal segment bears ventrally a slender clavate tail, 33 mm. long (fig. 23B). 



