Zool.-Vol. I.] JOHNSON— PACIFIC COAST ANNELIDS. 179 



but they are increased in size ; the dorsal setae are fre- 

 quently absent. The adaptation to the clinging function 

 is closest where the animal is obliged to maintain its hold 

 on the exterior of its host. So we find in P. fragilis and 

 P. pulchra that the setae are renewed as often as the tips 

 become at all blunted; in these two species the nascent setae 

 can generally be seen after clearing with oil, within the 

 ventral ramus of the foot (fig. 52). The setae of P. lordi, 

 on the contrary, are generally rather blunt at the tip. They 

 may become so in this species without danger, inasmuch as 

 the animal could maintain its place without clinging to its 

 host. 



P. pulchra has the habit of suddenly and forcibly extend- 

 ing the proboscis, which is sufficiently prehensile to enable 

 the animal to lay hold of its host. When two or three of 

 the worms are placed in the same dish they will often seize 

 hold of one another with such violence as to detach one or 

 more elytra from the region struck by the tip of the pro- 

 boscis. 



Polynoe" fragilis (Baird). 

 Plate VII, Figs. 36, 45; Plate VIII, Figs. 52, 52a, 526. 



Lepidonotus fragilis Baird. Proc. Zool. Soc. (London), April, 1863, 



p. 10S. 

 Halosydna fragilis Baird. Journ. Linn. Soc. (London), Vol. VIII, 



1865, p. 191. 



Form of body almost precisely like that of P. lordi, but a trifle broader 

 proportionately in the anterior third, and not so thick dorsoventrally. Elytra 

 continuing to extreme posterior end, which is much attenuated. Segmenta- 

 tion strongly marked, elytrophores and pseudo-elytrophores (on cirrus-bear- 

 ing somites) very prominent. 



Prostomium (fig. 36) short, rounded, broader than long; longitudinal fissure 

 continued to base; tentacle inserted in a deep notch anteriorly. All cirri 

 thick and fleshy, much clubbed at ends, very abruptly reduced to a ter- 

 minal filament. Antenna? very short, not exceeding length of prostomium, 

 two-jointed, joints of nearly equal length. Palpi short, acutely pointed, with 

 subterminal dark ring. Eyes four, small, placed back of median transverse 

 line. 



Parapodia (fig. 52) rather long, dorsal ramus setigerous, ventral cirrus 

 rudimentary or wanting. Dorsal setae few, serrated, notched at extremity 

 (fig.52*). Ventral setae only seven or eight, stout, hooked (52a), serrations 

 almost obsolete. 



