164 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 7 



A key to the species of Poecilochaetus Claparede 

 1. Dorsum conspicuously tubercled P. fulgoris 



1. Dorsum smooth or at least not tubercled 2 



2. Posterior segments provided with heavy spines that replace the dor- 

 salmost notopodial setae; lateral processes of nuchal organ greatly 

 elongated P. serpens 



2. Posterior segments without special spines; lateral processes of 

 nuchal organ reduced in length 3 



3. Dorsal and ventral cirri reduced, fingerlike from the twenty-first 

 segment; stout spines in median segments not known . P. tropicus 



3. Dorsal and ventral cirri continuing large through the median region, 

 the ventral cirri large throughout; median segments with stout, 

 blunt spines in notopodia and neuropodia . . P. johnsoni (see below) 



Poecilochaetus johnsoni, new species 

 Plate 30, Figs. 14-24 



Long, slender; length to 90 mm or over, width to 4 mm at tenth 

 setigerous segment or widest part. Body depressed, tapering gradually 

 posteriorly, the parapodia strictly lateral. Number of segments 150 or 

 over. Most of the integument is delicately punctate, but appears smooth 

 under low magnification. An area about the mouth and the ventral 

 surface of segments 1 and 2, and part of segment 3, is covered with 

 conical tubercles (pi. 30, fig. 18). They are continued in the mouth 

 and on the bases of the ventral cirri of the first segment. On the mid- 

 dorsum of segment 9 there is a dark, chitinous, diamond-shaped, elevated 

 structure. 



The prostomium is subspherical ; there are 2 minute eye spots near 

 the posterior margin, and 2 somewhat larger spots near the anterior 

 margin (pi. 30, fig. 17). Anteroventral margin with a median, cylindri- 

 cal antenna that projects forward between the first pair of setal fascicles. 

 A well-developed nuchal organ arises at the posterior margin of the 

 prostomium, its median elongation extends posteriorly to the sixth seg- 

 ment (preserved), its lateral lobes are less conspicuous swellings (pi. 

 30, fig. 17). There are 2 very long, grooved palpi inserted at the sides 

 of the prostomium. In life, they extend posteriorly to about the thirty- 

 first segment. They are held parallel to the sides of the body and lie 

 along the dorsum, just within the notopodial ridges. They autotomize 

 on fixation. 



