1921.] Fauna of the Chilka Lake : Polychaeta. 611 



distance, returns and traverses the branchia again, so that there appear to be four 

 vessels in the branchia. The branch to the ventral division of the foot terminates as 

 in the preceding species in a rounded ampulla. In a few of the anterior feet, branchiae 

 containing only a single loop were occasionally noted, but a double loop is the nor- 

 mal condition. The presence of two loops in the branchiae of this species may be 

 correlated with the relatively small number of branchiae. 



One of the abranchiate feet is shown in fig. 12c. In the posterior region of the 

 body the feet are large and deeply bilobed, the lobes being large, conical, and widely 

 divergent, giving a characteristic appearance to these specimens. 



The anus is terminal, and there is a single anal cirrus. Mature specimens, con- 

 taining ova and sperm, were taken in January, February, March and September, in 

 both the fresh and salt-water seasons. 



This species differs from N. polybranchia (1) in having 14 rows of papillae on the 

 proboscis, as compared with 22 ; (2) in having a long anterior unpaired papilla on the 

 median dorsal line of the proboscis ; (3) in the distribution of the branchiae, which 

 occur fully developed on the 6th foot, and disappear on the 20th to the 23rd foot, 

 whereas in N. polybranchia, the branchiae are large on the 5th foot, and persist 

 almost to the end of the body ; (4) in that the branchiae contain a double vascular 

 loop, whereas there is only a single loop in N. polybranchia ; (5) in that the posterior 

 lamellae of the feet are considerably surpassed by the spinal lobes. 



Habitat. — 18 specimens were collected in the Cochin Backwater, near Ernakulam, 

 in the south-west of the Madras Presidency. The salinity of the water is probably 

 very variable in this locality, but precise information is not available. 



In the Chilka Lake this species was taken at ten stations, all in the south-west 

 end of the lake, between Rambha and Nalbano. 



The species was apparently taken usually on a muddy bottom, both on the 

 shore, and dredged down to 15 feet. Eight stations were worked during the salt- 

 water season, and two during the freshwater season, but the gravity of the water in 

 this part of the lake only varies between the limits of 1-0015 and 1-0115. 



Family EUNICIDAE. 



Diopatra variabilis, sp. nov. 



(Plate XXV, figs. 14A-14R, and text-figs. i2a-e.) 



Of this species there are fragments, more or less complete, of seven large speci- 

 mens, all from the same station in Rambha Bay, and twenty- two small specimens 

 from various parts of the lake. The nature of the habitat, and the relation between 

 the large and small specimens, will be discussed below, when the large individuals 

 have been described. 



The largest (type) specimen, in three fragments, is 312 mm. long, composed of 451 

 segments. There is a short gap, probably consisting of about 20-30 segments, between 

 the first and second fragments, as is shown by the condition of the branchiae, and a few 

 posterior segments are missing, so that the animal originally had probably about 



