5j6 Memoirs of the Indian Museum. [Vol. V' 



however, in A . constricta, that the slender curved aciculum is present in all the f eet> 

 and that the sickle-shaped seta is an addition in the middle and posterior segments, in 

 the latter of which it is accompanied by a slender capillary seta. It is extremely 

 probable, therefore, that the sickle-shaped seta is a modified dorsal seta, and not an 

 aciculum. 



The A. albini of Langerhans (1881, p. 107) is quite distinct from any of these 

 species, if, indeed, it is a true Ancistrosyllis at all. 



Habitat. — This species was found on six occasions in the Chilka L,ake. Twice it 

 was taken in the outer channel, three times near the southern extremity of the lake 

 and once off Balugaon. 



On one occasion it was found in crevices of oyster shells at Manikpatna, but 

 usually it occurred on a muddy bottom in a few feet of water, and once it was taken 

 on a sandy bottom south of Mahosa. 



The salinity of the water varied from i-ooo-roiS, but the occurrence in the 

 outer channel at Manikpatna in oyster shells suggests that it can survive the salt- 

 water season when the gravity is as high as 1-026. 



Family NEREID AE. 



The wide variation usually to be observed in the structure of the parapodia from 

 various parts of the same specimen of Nereis necessitates a very close examination- 

 The difficulty of adequately representing the structure of the foot by the usual method 

 of illustrating the anterior and posterior aspects led to an attempt to depict it dia- 

 grammatically from the terminal aspect. In text-fig. 1, a typical foot from the right 

 side of a specimen of Nereis pelagica, I,. is shown from the anterior (A) and the 

 posterior (B) points of view and C is a diagram representing the same foot as it would 

 appear if examined from the terminal aspect. The arrangement of the various lobes 

 and different types of setae is obscure in A and B, but is clearly shown in C. The 

 position of the setae and their differing structure are indicated by the use of various 

 symbols. 



The posterior side of the foot is on the left of the vertical axis and the anterior 

 on the right. Thus the diagram represents the foot as it would appear if looked at 

 in situ on the right side of the worm, with the head to the right and the tail to the 

 left. 



Complete uniformity has not yet been attained in the nomenclature of the various 

 lobes which constitute the foot of a Nereid and the following explanation of the 

 terms here used may conduce to this end. There is considerable variation in detail in 

 the parapodia of the different species of the Nereidae, but the fundamental plan 

 remains fairly constant. The simplest and most typical form is seen in the sub- 

 genus Nereis, as represented by Nereis pelagica, T v . (text-figs. 1 a-c). Here the foot 

 consists of dorsal cirrus a, a ventral cirrus b, and three lobes designated in this 

 paper the dorsal ligule c, the median ligule d, and the ventral ligule e. Between the 

 dorsal and median ligules emerge the setae here known as " the setae of the dorsal 

 division." Where they emerge from the foot, these setae are surrounded by a mem- 



