I9 21 -] Fauna of the Chilka Lake : Polychaeta. 609 



In the 3rd foot the lamellae are more prominent, the branchia is rather larger, 

 and there is a slight indication of the dorsal cirrus. The anterior row of setae in the 

 ventral division are mostly barred, but a few smooth setae occur at the upper and 

 lower ends of the row. The setae are now in two rows, before and behind the spines, 

 not above and below them as in the ist and 2nd pairs of feet. The 4th foot is very 

 similar, but a distinct change occurs in the 5th foot, which is almost normal. The 

 branchia is large and thick, with a small cirrus on its upper basal portion. The 

 normal condition of the anterior feet is shown in fig. iid (also text-fig. 116) of the 

 10th foot. The spines, which are ringed at the tip, terminate in each division at the 

 tip of a conical papilla, which is surrounded by a ring of setae. The setae in front 

 are of the usual camerated type, rather short and stout. The posterior setae are very 

 long and slender capillary setae, with slightly flattened blades very finely serrated 

 along one edge (fig. iif). They are more numerous than the camerated kind, and 

 tend to invade the front row at the upper and lower ends of the bundles. Surround- 

 ing the setae is a fillet which, in both divisions, projects a little beyond the spine on 

 the posterior side of the foot, but not on the anterior side. In the dorsal division the 

 lower ends of the fillet are attached to the branchia, in the ventral division to the 

 ventral cirrus. The dorsal cirrus is small but distinct. The vascular system of the 

 foot consists of a vessel which traverses the branchia as a single loop (fig. iid). 

 On emerging, it divides, and the smaller branch runs down to the ventral divi- 

 sion. It then curves back and terminates in a flask- shaped ampulla. 



In fully grown specimens the barred setae are found only in the anterior 16 feet, 

 whilst smaller specimens may have them in 12-15 feet- They are then replaced by 

 smooth capillary setae (fig. 11G), which are smaller than those in the posterior row. 

 The blade widens rather suddenly, and then tapers to a fine tip. The 20th and 30th 

 feet (fig. HE) are very similar, except that the anterior dorsal lobe of the fillet is rather 

 larger, the posterior lobes are smaller, and the branchia is relatively very large. In 

 the posterior feet the fillets are small, and are considerably surpassed by the spinal 

 lobes. At the 45th foot the branchia suddenly becomes small, and is absent on the 

 succeeding 7 posterior segments. 



The anus is terminal, and there is a single short tapering anal cirrus. 



This species is characterised by the structure of the proboscis, the shape of the 

 head, and by the condition of the feet. As regards the latter, the most important 

 characters are the size and shape of the lamellae ; the restriction of the camerated 

 setae to the anterior feet, and their replacement in the middle and posterior feet by 

 peculiar capillary setae ; the distribution of the branchiae, and the presence in them 

 of only a single vascular loop. 



Habitat. — The 12 specimens, all mature or approaching maturity, were taken at 

 4 stations, all in the south-west end of the lake between Rambha and Nalbano, the 

 shore being mud or sandy mud. Two of the stations were worked in February, the 

 salt-water season, and two in September and November, the freshwater season, but 

 in this part of the lake the specific gravity only ranges from rooi-roii5 



