1921.] Fauna of the Chilka Lake : Polychaeta. 651 



these setae are longitudinally striated, and some are smooth, whilst others have the 

 terminal part of the shaft covered with fine short hairs. 



The three anterior segments of the body have two bundles of setae each. 

 There are 14-26 setae in each bundle, the youngest being on the ventral margin 

 of the bundle. The setae have a double curvature, and are longitudinally striated 

 the striations being in the superficial layer. The core of the seta is abruptly 

 truncated some distance from the tip (fig. 5B). This appearance is not caused by 

 injury, as it was observed in cases where the seta tapered to a fine point. 



Distribution. — Miya Bay, Japan ; Bai von Batavia, in mud, 10-12 fms. 



Habitat. — 316 specimens were taken at four stations in the outer channel near 

 Mahosa, in September, when the water was quite fresh. The bottom here is sand 

 and sandy mud. Mr. Kemp says in litt. : "As regards the Sternaspis, we only found 

 it in the outer channel at the season when the water was quite fresh. But our 

 observations in March were a little incomplete, for the water was too shallow to 

 permit the passage of the launch across the bar separating the main area from the 

 outer channel, and we had only a dinghy to work from. The species is doubtless 

 present all the year round in salinities varying from 1/000 to i - o27." 



Family SABEUJDAE. 



Potamilla leptochaeta, sp. nov. 



(Plate XXXI, figs. 28A-N.) 



A number of small specimens of this species were found in masses composed of 

 Entoproct Polyzoa (Loxosomatoides colonialis, Annandale), accompanied by Bowerban- 

 kia caudata, Hicks, and by a number of Nematode worms (Oncholaimus indicus, von 

 Ivinstow, Rec. Indian Museum, Vol. I, 1907, p. 45). 



The Potamilla lives in rather brittle membranous tubes, coated with fine mud, 

 very like those of P. torelli } but not quite so hard and hyaline. The stolons of 

 the Polyzoan are attached to the worm tubes, the whole forming a tangled mass. 



Most of the specimens are incomplete, the posterior extremity usually being 

 absent. A moderate sized individual, not the largest, measured 45 mm. in length, 

 of which the branchiae were 13 mm., the thorax 12 mm., and the abdomen 2 mm. 



The branchiae are marked by two broad bands of reddish brown pigment. 

 The total number of setigerous segments is about 33 or 34, of which 6 compose the 

 thorax, and 27 or 28 the abdomen. The thorax is of uniform width, but the abdo- 

 men tapers gradually towards the anal segment. The latter is rather flattened, 

 and heart-shaped, with rounded posterior border. No eyes were observed, either 

 on the anterior or anal segments or on the branchiae. 



In all specimens examined, there were 9 branchiae, 4 on the right side, 5 on the 

 left. Each branchia has 40-50 filaments. The latter are nearly all of the same 

 length, decreasing slowly in size towards the tip. In most of the specimens the tip 

 is short, bare, and blunt (fig. 28c), but one specimen was found in which all the 

 branchiae had rather long bare tips (fig. 28d). A more careful examination then 

 showed that branchiae with long tips were by no means uncommon, even in speci- 



