76 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 25 



The prostomium is about 3 times as wide as long, widest at the 

 mid-length, and has 4 red eyes in a nearly transverse row on the dorsal 

 side. The gizzard, seen through the body wall, is short cylindrical, 

 located in 3 successive segments, and resembles that of Sphaerosyllis 

 species. The posterior third of the body is opaque white, filled with 

 gonadial products. The 3 prostomial antennae are short, globular, 

 f rontally attached and well separated from one another ; these, together 

 with the peristomial cirri, are slightly larger than dorsal cirri of body 

 segments, but otherwise similar. 



Parapodia are compressed and overlap those of adjacent segments, 

 reminiscent of the elytra of scale-worms. They are uniramous, supported 

 by single, thick, yellow acicula that taper distally and terminate in a 

 slightly falcate tip. The projecting setae, numbering 10 to 15 in a 

 fascicle, are of a single kind. All are composite, falcigerous, and the 

 distal appendage is entire and has a dentate cutting edge (PL 33, fig. 1) ; 

 the shaft is smooth, much thicker than the appendage and widest in 

 a transverse direction so that its greatest width is not observed when the 

 appendage is seen in lateral view. 



Plakosyllis americana is to be compared with only one other species, 

 P. brevipes Hartman-Schroder (1956, p. 87) described from the 

 Mediterranean Sea. The latter measures 1.5 to 3 mm long, consists of 

 40-44 segments and has eyes in trapezoidal arrangement. P. americana 

 consists of 75 to nearly 100 segments, is longer, and the details of com- 

 posite falcigers differ. 



P. americana has been taken off southern California, in red sands, 

 associated with Branchiostoma (a lancelet), Hemipodus borealis John- 

 son, species of Sphaerosyllis, and numerous other kinds of polychaetes. 



Genus Odontosyllis Claparede, 1863 

 Type O. fulgurans (Audouin and Milne Edwards) 1833 



Odontosyllis phosphorea Moore, 1909 



Odontosyllis phosphorea Moore, 1909, pp. 327-329, pi. 15, figs. 8-10; 



Berkeley and Berkeley, 1948, p. 82. 

 Hesperalia calif orniensis Chamberlin, 1919, p. 9. 



Collections. This species occurs frequently in southern California, 

 in shallow depths, in rocky habitats with kelps and encrusting growths. 



Length of mature individuals is 20 to 30 mm. The dorsum is pale ivory 

 or yellowish and is crossed by broad black bands. The large nuchal flap 

 is dark and covers much of the prostomium, including the 4 large, 



