EREANTIATE TOLYCHAETA OF JAPAN. 169 



U ; it is provided witli four pairs of setigerous parapodia, a pair 

 of tentacles, a pair of tentacnl arcirri and a pair of short anal 

 cirri. Tlie two pairs of the " Anlagen " of eyes are dis- 

 tinctly seen on the postero-lateral parts of the head ; a pair of 

 jaws, each witli three teeth, may also be seen abeady in this 

 stage of development. 



The embryos, at about this stage of development, begin to 

 sink down gradually in the water, in which they have been reared ; 

 and about two days later, most of them are on the bottom 

 and liave entered into sedentary life. 



Nereis dyaniiisi n. sp. 

 PJ. XVIIl, figs. 1—7. 



Body elongate, broadest in the anterior one-third of its 

 length ; up to 250 segments. Length of mature worms 340-490 

 mm. ; breadth 11 — 13 mm., or 20 — 24 mm. including parapodia 

 and bristles. Prostomium longer tlian broad ; tentacles scarce- 

 ly i- the length of the prostomium, meeting one another at 

 their base ; palpi extending beyond tentacles. ï'irst body- 

 segment twice as long as the succeeding ; its anterior border 

 sliglitly overlaps the prostomium in the middle, being convex for- 

 ward. Iiifciior tentacular ciri-i slightly shorter than palpi, tlie 

 superior ones longer tlian tlie latter ; longest tentacular cirri 

 read ling to 8 th segment. 



I'aiapodiiiiii nearly uniform, the two rami in anteriorly placed 

 parapodia more ('losely set than in posteriorly placed ones ; dorsal 

 ramus witli two lips, of which the larger one is conical and as 

 long as the inferior lip of ventral ramus in anteriorly placed 



