1904.] 



MARINE FAUXA OF ZANZIBAR. 



329 



The feet of the anteiior pai't of the body project eoiisideiubly, 

 th.ose of the posterior very little. The former ;ip]ieai' to be thicker 

 distally than at their bases, owing to tlie breadth and thickness of 

 the lips of the seta-sac and to the swelling of the ventral cirri to 

 an egg-shape, the bi'oad end being the distah The posterior feet 

 are as usual pointed at their tips and have small, scarcely visible 

 ventral cirri. In this way is caused the more striking of the 

 dijfferences between the anterior and posterior parts of the body, 

 the change taking place quite rapidly at the point mentioned, 

 at which also a two-hooked a-cicular seta first appears. In the 

 antei'ior feet the dorsal cirrus is long, projecting beyond the end 

 of the seta-sac ; posterioi-l}' it is very small (compare the figures 

 of the feet in text-fig. 66). 



Text-fio'. 66. 



Antevior and hinder feet of Nieidion gracUis. X 60. 



The seta? are numei'ous and pi-oject well anteriorly when not. 

 as is frequently the case, bi-oken ofi' level with the end of the 

 seta-sac. This is the case almost always posteriorly, where usually 

 only a few comb-setfe are found pi-ojecting. All ai-e of the usual 

 form and their details are given in fig. 11, PI. XXII. 



There is a single pair of shoi't and slender anal cirri. 



This species is very closely isolated to iT. hrevis Ehlers, from 

 which it is distinguished at once, however, by the slenderness and 

 anterior compression of its body, the shortness of its tentacles, 

 and form of its teeth. The resemblances between the two species 

 are certainly more striking than the diiFerences, comprising the 

 smallness of the tentacular cirri, broad features of the jaw- 

 apparatus (including apparently the remai'kable delicacy of the 

 lower jaws), structui-e of the feet and setse, and the characteristic 

 differences betAveen those of the anterior and posterior portions of 

 the body. 



