290 Dr. Johnston on the British Nereides. 



various species^ and distributed in annular rows or limited 

 patches : the orifice is destitute of tentacula, but armed with 

 two powerful jaws curved like a sithe and serrulated on the 

 inner margin (fig. 1 a, pr,)» The first segment of the body 

 (fig. cit. s.) is often larger than the follow ing ; and from its 

 anterior margin four pairs of tentacular cirri arise [t), which 

 spread out on each side of the head in the form of tapered 

 filaments. The feet are homologous throughout and protu- 

 berant^ formed of two branches coalescent at their insertion 

 with the trunk ; and each branch is furnished with a spine^ 

 or sometimes with two or three spines^ and one or two bun- 

 dles of bristles (fig. 1 b.) : the latter are two-jointed^ the basilar 

 portion being thickened towards its extremity^ which is deeply 

 cleft to receive the terminal piece into a sort of socket (fig. 

 1 c.) : this piece is sometimes long^ straight^ and subulate^ at 

 other times shorty flattish, and slightly curved. The cirri are 

 always slender and tapered ; we find one at the base of each 

 branch of the foot, and that of the ventral branch is invariably 

 shorter than the one pertaining to the dorsal (fig. 1 b, c). 

 The branchiae, according to Savigny, are constituent parts of 

 the feet, consisting of three fleshy papillae which occupy their 

 extremity (fig. 1 b, b.). Two of these lobe-like appendages are 

 fixed to the dorsal branch, one under the superior cirrus and 

 one under the setigerous tubercle ; and the third is situated 

 under the ventral branch, between the setigerous tubercle and 

 inferior cirrus. The form of these papillae, as well as their 

 relative size, often varies on the different parts of the body, 

 but they are found on all the feet, excepting, sometimes, on the 

 second and third pairs, where they are more or less rudiment- 

 ary. Audouin and Milne Edwards deny their branchial cha- 

 racter, since they are not more vascular than the other lobules 

 of the foot ; but at the base of these organs there is a vascular 

 net-work, which appears to the naturalists mentioned to be 

 the principal seat of respiration. The anal segment is always 

 terminated with two styles. 



1. iV. pelagica, body brownish, more or less tinted with 

 green ; post-occipital segment nearly twice as large as the fol- 

 lowing ; cirri shorter than the pa illary processes of the feet, 

 Plate VI. fig. 1. 



