646 Memoirs of the Indian Museum. [Vol. V, 



ventral groove, help to form two ventro-lateral ridges, containing the stout longi- 

 tudinal neural muscle bands. 



The tori in segments 2-4 are very short, containing about 20-30 setae. Segment 

 5 has rather longer tori, and on the 6th and subsequent segments the tori are 3-4 

 times as long, and contain 50-60 setae. There is no very obvious external difference 

 between the posterior thoracic and the anterior abdominal segments. The latter are 

 divided into two rings, a smooth anterior and a slightly enlarged posterior ring, the 

 latter bearing the tori with their tumid lips. 



The setae of segments 2-4 are rather short, with pointed tips, bilimbate, with 

 narrow wings. The ventral setae closely resemble the dorsal setae (fig. 25B), and 

 they are very similar to the capillary setae of Barantolla sculpta. The thoracic setae 

 are all capillaries with the exception of two in the right ventral bundle of the 12th 

 segment (nth foot). This bmdle contains 45 setae, of which 43 are normal capil- 

 laries. The other two are elongate hooks, very similar to those in the posterior 

 thoracic segments of Barantolla sculpta. The nodulus is only slightly indicated. It is 

 well in the distal half of the shaft, thus differing somewhat from the similar setae of 

 Barantolla sculpta. The shaft is widest near the lower end of the wing, and narrows 

 gradually towards the neck, beneath the hooked tip. In the absence of any marked 

 widening of the shaft below the neck, these setae resemble those of Barantolla sculpta 

 and differ from those of Heteromastus similis (compare figs. 23G, 24G and 25c). 

 The tooth at the tip is rather slender, and makes an obtuse angle with the shaft. 

 Behind the tooth the crest bears 5 or 6 slender spines. These setae are -52 mm. long, 

 a little shorter than the capillaries of the same bundle, which are *6 mm. long. 

 Except for the hooked tip, they greatly resemble the capillary setae in general 

 appearance. No other crochets were found in the thoracic tori. The setae of the 

 corresponding ventral bundle on the left side of the body were all broken, except a 

 few, which had capillary tips. In the nth segment all the setae were capillaries. 

 Owing to the lack of material it is impossible to elucidate the significance of the pre- 

 sence of these two elongate crochets. The resemblance they exhibit to the similar 

 setae in the posterior thoracic segments of Heteromastus and Barantolla indicates the 

 close affinity existing between these three genera, and their presence in this specimen 

 may represent a reversion to an ancestral type which possessed them normally in the 

 posterior thoracic segments. On the other hand it is possible that these setae occur 

 normally in the young and immature stages of Mastobranchus indicus, and are replaced 

 by capillaries as the individuals approach maturity. 



The dorsal bundles of the 13th and 14th segments each contain about 40 capil- 

 lary setae, similar to those in the thoracic feet, and there are no crochets accompany- 

 ing them. The ventral bundles contain only crochets, about 40 in each bundle. 

 These differ considerably from those in the last thoracic ventral bundle (figs. 25D, 

 25E). The nodulus is distinct, in the distal part of the shaft. The shaft shows a 

 distinct swelling below the neck. These setae are only -28 mm. long. The wing, 

 enclosing the tip, is relatively short. The terminal tooth makes rather a wide angle 

 with the shaft, and on the crest behind it are two transverse rows of spines. In the 



