1921.] Fauna of the Chilka Lake : Polychaeta. 575 



small and straight, just reaching the base of the dorsal cirrus. In the 5th foot it is 

 much longer, passing into the cirrus, but not piercing the epidermis. In the 10th 

 foot all the setae show at least traces of serrations, and the anterior setae have longer 

 teeth than those in the example figured from the ist foot. In the 20th foot the dor- 

 sal spine is curved at the tip, but still completely embedded in the foot. There are 

 two minute papillae on the base of the dorsal cirrus. The setae in the upper group 

 are longer than those in the lower group, and the number of coarsely serrate setae is 

 relatively less. 



Between the 30th and 40th feet a stout sickle-shaped seta appears in the dorsal 

 division (fig. id). It is in addition to the dorsal spine, which still persists, thin and 

 curved, and does not pierce the epidermis. Ehlers (1908, p. 60) says that in A . robusta, 

 the stout sickle-shaped seta replaces the slender spine. The sickle-shaped seta tapers 

 gradually towards the tip, which pierces the skin, and there is no nodulus such as 

 Macintosh shows in A. groenlandica (1877, pi- 65, fig. 3). Behind it are a few small 

 conical papillae on the base of the dorsal cirrus. 



The succeeding feet do not show much change. In the posterior 27 feet of the 

 specimen examined the spine and hook of the dorsal division are joined by a slender 

 capillary seta (fig. iE) which pierces the skin. The spine tapers very rapidly near 

 the curved tip. The papillae on the base of the dorsal cirrus are larger and more 

 numerous than in the anterior and middle feet, and the setigerous lobe is shorter and 

 more rounded. The anus is terminal, and the anal segment bears two slender ventro- 

 lateral cirri, equal in length to the last six segments. 



A specimen with the body-cavity full of ripe sperm was found in September, in 

 the Outer Channel, during the freshwater season. 



This species greatly resembles in many respects the A. robusta, Ehlers (1908, 

 p. 59), found at Great Fish Bay, S.W. Africa, but differs in the following characters :— 

 (1) the shape of the body ; (2) the palps are fused almost throughout their length, 

 and are flat, not cylindrical ; (3) the ist foot has a well-developed setigerous lobe, 

 and the dorsal cirrus is 3^ times as long as the ventral cirrus. In A . robusta the seti- 

 gerous lobe is small, and the dorsal cirrus twice as long as the ventral ; (4) the papil- 

 lae on the base of the dorsal cirrus, and the dorsal capillary seta of the posterior 

 feet were not observed by Ehlers in A. robusta; (5) the proboscis has 14 papillae, 

 that of A . robusta 16 ; (6) the absence of the ventral cirrus of the second pair of feet 

 is not mentioned by Ehlers nor Macintosh. 



The .4. groenlandica of Macintosh (1877, p. 502), dredged in 410 fathoms in Davis 

 Strait, is very different from A . constricta or A . robusta, but in several characters of 

 the feet it shows the greater affinities with the former species. The setigerous lobe 

 and dorsal and ventral cirri bear many small cylindrical papillae. More important, 

 however, is the presence in the dorsal division, together with the stout sickle- shaped 

 seta, of a slender bristle, generally enclosed in the tissues. According to Ehlers the 

 sickle-shaped seta is a modified, aciculum, which, in A. robusta, has replaced the 

 simple curved spine of the anterior segments, and he does not regard the presence of 

 both forms in the same foot in A. groenlandica as affecting this theory. It is clear, 



