1921.] Fauna of the Chilka Lake : Polychaeta. 645 



than the abdominal crochets in shape, with only a slight expansion below the neck, 

 but they have short wings over the tips, and the nodulus is in the distal half, though 

 only slightly developed. The length of these crochets is as follows : — 



On the 8th segment, '33 mm. 



„ „ 13th „ , -25— -26 mm. 



„ „ 14th „ , -15— -17 mm. 



,, ,, 60th ,, , -05 — -06 mm. 



Passing towards the tail the abdominal setae become fewer and smaller. In the 

 13th foot there are 25 in a bundle, on the 60th foot 10, and on some of the posterior 

 feet 2 or 3, or none at all. The spines on the crest of the crochets form a transverse 

 curved row, the concavity facing the terminal tooth. 



Habitat. — This species was collected in some brackish pools near the salt lake at 

 Barantolla, near Calcutta, in November. The salinity of the water is very variable, 

 but never high, probably never exceeding i'oi5. 



Mastobranchus indicus, sp. nov. 

 (Plate XXX, figs. 25A-F.) 



This description is founded on a single specimen from brackish pools, near 

 Barantolla. Unfortunately only the anterior end is available, in a very contracted 

 condition. It is 46 mm. long, and consists of 90 segments. The widest part is near 

 the anterior end, where it is 3 mm. wide. The fragment evidently belongs to an 

 individual considerably larger than the specimens of Barantolla sculpta. 



The head (fig. 25A) consists of a small rounded lobe, withdrawn under the 

 buccal segment. No trace of eyes or nuchal organs could be found. The skin of 

 segments 1-6 and the anterior part of 7 is tessellated, the grooves being deeper in 

 the anterior segments. The thorax consists of 12 segments, of which the ist is 

 achaetous. The sculpturing of the thorax recalls that of Barantolla sculpta (compare 

 fig. 25A and fig. 24A), but is not so distinct or general. On the ventral surface 

 hexagonal areas occupy the median line in segments 5-8 and the anterior part of 9. 

 The ventro-lateral narrow hexagonal areas are clearly differentiated on segments 

 6-9, less clearly on segments 3-5. In segments 10-13 these areas gradually coalesce 

 with the tumid tips of the ventral tori. The lateral organs are not very distinct, 

 but narrow hexagonal areas, clearly marked off by grooves, lie between the dorsal 

 and ventral setae in segments 5-8. They probably exist in other adjacent segments, 

 but are not distinctly differentiated in this specimen. On the dorsum narrow trans- 

 verse hexagonal areas occur between the dorsal bundles of setae in segments 5 -11 - 

 As is the case with all the other areas, lateral and ventral, it is the posterior groove 

 which disappears first, the anterior grooves remaining on many posterior segments, 

 forming a complete groove round each segment. Four pairs of genital pores were 

 observed, behind segments 8-1 1. In the lateral region there is a deep groove on 

 each side, commencing in the 6th segment, and these, combined with a shallow 



