74 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 10 



through the tenth setiger; thereafter they are exceeded in size by the 

 branchial filaments. 



Branchiae are first present from the sixth setiger, already with 3 

 small filaments; the next 2 setigers have 3 longer filaments on each, a 

 ninth parapodium has 4 filaments, continuing so through the thirteenth 

 setiger. The number of filaments increases gradually to 8 on the fifty- 

 eighth setiger, and the branchia is continued as a strong, pectinately 

 branched structure through a long region. The posterior end or post- 

 branchial part is missing. 



Anterior parapodia through the fifth setiger are provided with tri- 

 dentate hooded hooks (pi. 3, fig. 65) ; a second parapodium has 4 such 

 hooks, with weak articulation ; hooks are accompanied by several fine, 

 pointed, bilimbate setae. From the sixth setiger the ventralmost setae 

 consist of composite spinigers (pi. 3, fig. 63) numbering 3 or 4 in a 

 fascicle; these continue to be present through about the nineteenth or 

 twentieth setiger and are accompanied by 5 to 7 similar, simple setae, 

 and 10 to 15 longer, slenderer, narrowly bilimbate setae, progressively 

 upward. In a seventh parapodium there are also 4 pale acicula, each with 

 acute tip (pi. 3, fig. 66). The composite spinigers are thereafter replaced 

 by a heavy subacicular hook. No simple, heavy acicular hooks have been 

 observed. The subacicular hooks are distally bidentate (pi. 3, fig. 64) ; 

 they occur singly in the nineteenth or twentieth setiger, but thereafter 

 2 in a fascicle. Pectinate setae are slender, delicate, in inconspicuous 

 fascicles of 3 to 5 ; the flaring end is slightly oblique, the pectinate edge 

 with 15 to 20 fine, long teeth. Acicula are yellow, sharply geniculate, 

 prolonged to a slender point that projects from parapodia; they number 

 4 in a parapodium in anterior segments and 3 in median segments. 



The proboscidial armature is weakly developed, translucent, with 

 dark horny articulations, and the distal plates of the mandibles are white, 

 calcareous. The maxillary carriers taper basally to blunt points (pi. 3, 

 fig. 61 ). The formula of the plates is as follows: On the left side maxilla 

 I is falcate, II has 9 teeth, III has 9 teeth, IV has 7 teeth, and V has a 

 single tooth. On the right side I is falcate, II has 9 teeth. III (with fused 

 IV) has 11 teeth, V has a single tooth. On plates III and IV the 3 to 5 

 distalmost teeth are slightly the largest and the others are gradually 

 smaller. The mandibles have long, slender, translucent ends and broadly 

 rounded distal plates (pi. 3, fig. 62). 



O. peruana belongs to a group in which anterior hooks are distally 

 tridentate ; to it belong also O. eremita, O. zebra, and O. litoralis 

 (above). O. peruana differs from O. eremita in that branchiae are first 



