EREANTIATE POLYCHAETA OF JAPAN. 113 



Body YOiy large, measuring one metre or more in length and 

 about 20 mm. in lireadth at tlio widest region. Number of segments 

 u]) to 430. In tlio anterior region of body the segments are highly 

 arched dorsal ly, and gradually become low-arched toward the poster- 

 ior end. Tlie colour of the living animal is black with strong metallic 

 iridescence, and usually the 6tli and 7th segments are lighter 

 coloured. 



Prostomium with 5 smooth tentacles, the median being the 

 longest and reaching to the anterioi' margin of 3rd segment ; 

 the inner laterals shorter, reaching to tlie anterior margin of 

 2nd segment ; the outer laterals still slightly shorter. Eyes 2, 

 each being situated between and a little behind the bases of 

 the inner and outer lateral tentacles. Anterior margin of pro- 

 stomium divided into 4 lobes, those of the inner pair being 

 pear-shaped and constricted from the outer broad, ventro -laterally 

 directed lobes. 



The first segment almost 3 times as long as the next follow- 

 ing, which is marked off from the ßrst only in the dorsal aspect ; 

 the second segment provided with 2 short and smooth ten- 

 tacular cirri. 



Parapodium (fig. 3) with a smooth and slender dorsal, and a 

 short and conical ventral, cirrus. 



Bristles are of tlireo kinds ; the dorsal group consists of 

 simi>b setose (fig. 4) and slender pectinate (fig. 5) bristles, while 

 1Iie Nctifral group is made u]) of stout compound bristles, of which 

 tlie slioi't and stout end-piece is jirovided with 2 teeth (fig. 0). 

 Acicula black : usually 3, i-arely 2, in each parapodium. 



P)raiiehiae pecliiiate, begin to occur on 8th — 10th segment 

 as a sinijilr lilameui, hut are soon divided, attaining maximum 

 devel('imi('iit (Ml alioul r)Otli segment, where the branchial fila- 



